The influence of streptozotocin-induced diabetes and the antihyperglycaemic agent metformin on the contractile characteristics and the membrane potential of the rat diaphragm

We studied the effect of aminophylline (0.1–1 mM) on the contraction threshold (CT) of rat diaphragm fibers (25 degrees C). The CT was measured by direct visualization (x200) of the fiber under current-clamp conditions. The main findings are the following: 1) Aminophylline lowers the CT, in a dose-dependent manner, toward more negative values of the resting membrane potential (Vm). 2) Dibutyryl adenosine 3′,5′-cyclic monophosphate (2 mM) shifts the CT, although this change is smaller than in the presence of xanthine. 3) Tetracaine (1 mM), a drug that diminishes Ca release from the sarcoplasmic reticulum, reduces the shift induced by 1 mM aminophylline; this is partially overcome by increasing aminophylline concentration to 5 mM. 4) Hyperpolarization of the fibers shifts the CT to more negative Vm. We suggest that the displacement in the CT to more negative Vm plays an important role in the potentiating effect of aminophylline. This could be the result of an enhancement of Ca release from the sarcoplasmic reticulum.

Download Full-text

The effect of glutamate and inhibitors of NMDA receptors on postdenervation decrease of membrane potential in rat diaphragm

Molecular and Chemical Neuropathology ◽

10.1007/bf02815179 ◽

1998 ◽

Vol 33 (3) ◽

pp. 163-174 ◽

Cited By ~ 6

Author(s):

A. Kh. Urazaev ◽

N. V. Naumenko ◽

G. I. Poletayev ◽

E. E. Nikolsky ◽

F. Vyskočil

Keyword(s):

Membrane Potential ◽

Nmda Receptors ◽

Rat Diaphragm

Download Full-text

Effect of aminophylline-Ca2+ blocker interaction on membrane potential of rat diaphragm fibers

Journal of Applied Physiology ◽

10.1152/jappl.1993.74.6.2745 ◽

1993 ◽

Vol 74 (6) ◽

pp. 2745-2749 ◽

Cited By ~ 5

Author(s):

O. Delbono ◽

B. A. Kotsias

Keyword(s):

Membrane Potential ◽

Calcium Channel ◽

Calcium Channel Blockers ◽

Intrinsic Activity ◽

Resting Membrane Potential ◽

Maximum Effect ◽

Channel Blockers ◽

Dependent Manner ◽

Rat Diaphragm

We studied the antagonism between aminophylline and two calcium channel blockers, nifedipine and verapamil, and its effect on the resting membrane potential of rat diaphragm fibers in vitro at 25 degrees C. Aminophylline hyperpolarizes the fibers in a dose-dependent manner, and the maximum effect is reached with 1 mM of the drug, approximately 9 mV compared with normal values. Both nifedipine and verapamil (1–5 microM) decreased the amount of hyperpolarization induced by aminophylline, and this is partially reversed when the xanthine concentration in the bath is increased. From the Hill equation we obtained a value of 2 for the slope, suggesting that two molecules of aminophylline bind to the receptor. Nifedipine modifies the affinity and the intrinsic activity of aminophylline, whereas verapamil reduces its intrinsic activity. The effect of nifedipine and verapamil is explained on the basis of the changed action of aminophylline on its site as a result of the interaction of the calcium channel blockers with their interdependent receptors.

Download Full-text

Chronic Actions of Nicotine on the Electrogenic Activity of Na+,K+-ATPase and the Contractile Characteristics of Rat Diaphragm

Neuroscience and Behavioral Physiology ◽

10.1007/s11055-013-9800-6 ◽

2013 ◽

Vol 43 (6) ◽

pp. 723-729

Author(s):

A. N. Vasil’ev ◽

V. V. Kravtsova ◽

I. I. Krivoi

Keyword(s):

Rat Diaphragm ◽

Contractile Characteristics

Download Full-text

Detrimental Effects of Short-term Glucocorticoid Use on the Rat Diaphragm

Physical Therapy ◽

10.1093/ptj/80.2.160 ◽

2000 ◽

Vol 80 (2) ◽

pp. 160-167 ◽

Cited By ~ 10

Author(s):

Jane M Eason ◽

Stephen L Dodd ◽

Scott K Powers ◽

A Daniel Martin

Keyword(s):

Control Group ◽

Rat Diaphragm ◽

Drug Injection ◽

Short Term ◽

Glucocorticoid Treatment ◽

Injection Period ◽

Specific Tension ◽

High Doses ◽

Tetanic Tension ◽

Contractile Characteristics

Abstract Background and Purpose. The purpose of this study was to determine the effect of short-term, high doses of glucocorticoids on both body and diaphragm weights as well as contractile characteristics of the rat diaphragm. Subjects. Adult, female Sprague-Dawley rats were divided into 2 groups: a control group (n=16) and a prednisolone group (n=16). Methods. The prednisolone group received prednisolone at a dosage of 5 mg/kg, and the control group received sham saline injections for 5 days. Animals were weighed prior to and after completion of the drug injection period. At the completion of the drug injection period, the animals were sacrificed, and the diaphragm, soleus, and extensor digitorum longus muscles were removed and weighed. A small strip of the costal diaphragm was connected to a force transducer, and the following contractile characteristics were measured: maximal specific isometric tetanic tension, peak isometric twitch specific tension, one-half relaxation time, and time to peak tension. Results. Both body and diaphragm weights decreased by 15% in the prednisolone group as compared with the control group. Maximal specific isometric tetanic tension was reduced 13% in the prednisolone group as compared with the control group. There was no difference in any twitch contractile characteristics between the 2 groups. Conclusion and Discussion. These data support the hypothesis that glucocorticoid treatment over a 5-day period results in a decrease in specific tension as well as diaphragm and body weight. These results may have implications for the treatment of patients receiving high doses of glucocorticoids for acute medical conditions.

Download Full-text

Effect of aminophylline on mechanical activity of rat diaphragm bundles

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.3.1142 ◽

1990 ◽

Vol 68 (3) ◽

pp. 1142-1149 ◽

Cited By ~ 7

Author(s):

O. Delbono ◽

B. A. Kotsias

Keyword(s):

Membrane Potential ◽

Calcium Release ◽

Principal Factor ◽

Mechanical Activity ◽

Resting Membrane Potential ◽

Direct Visualization ◽

Rat Diaphragm ◽

Mechanical Threshold ◽

Rate Of Decay

We studied the effect of aminophylline (0.1-1 mM) on the mechanical and electrical activity of rat diaphragm bundles in vitro (25 degrees C). The main findings are the following. 1) Aminophylline potentiates the twitch tension. The tetanus tension is not modified, although the rate of decay is decreased. 2) The relation between K contracture tension and resting membrane potential (Vm) is shifted toward more negative values of the Vm in the aminophylline-containing solution. 3) The mechanical threshold measured by direct visualization of the fiber is also lowered in the fibers equilibrated in aminophylline. These effects are reversible by washing out the preparation with normal solution. 4) The shift in the relation between tension and Vm induced by aminophylline is reversed by 1 microM nifedipine. 5) The generation of action potential is not modified by aminophylline. We suggest that the shift in the mechanical threshold is the principal factor involved in the potentiating effect of aminophylline. We speculate that theophylline acts to augment tension by enhancing calcium release from the sarcoplasmic reticulum and that nifedipine blocks this release (E. Rios, and G. Brum. Nature Lond. 325: 717-720, 1987).

Download Full-text