Ionic Basis of Smooth Muscle Action Potentials

Freshly dispersed sheep mesenteric lymphatic smooth muscle cells were studied at 37°C using the perforated patch-clamp technique with Cs+- and K+-filled pipettes. Depolarizing steps evoked currents that consisted ofl-type Ca2+ [ I Ca(L)] current and a slowly developing current. The slow current reversed at 1 ± 1.5 mV with symmetrical Cl− concentrations compared with 23.2 ± 1.2 mV ( n = 5) and −34.3 ± 3.5 mV ( n = 4) when external Cl− was substituted with either glutamate (86 mM) or I− (125 mM). Nifedipine (1 μM) blocked and BAY K 8644 enhanced I Ca(L), the slow-developing sustained current, and the tail current. The Cl− channel blocker anthracene-9-carboxylic acid (9-AC) reduced only the slowly developing inward and tail currents. Application of caffeine (10 mM) to voltage-clamped cells evoked currents that reversed close to the Cl− equilibrium potential and were sensitive to 9-AC. Small spontaneous transient depolarizations and larger action potentials were observed in current clamp, and these were blocked by 9-AC. Evoked action potentials were triphasic and had a prominent plateau phase that was selectively blocked by 9-AC. Similarly, fluid output was reduced by 9-AC in doubly cannulated segments of spontaneously pumping sheep lymphatics, suggesting that the Ca2+-activated Cl− current plays an important role in the electrical activity underlying spontaneous activity in this tissue.

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Variations in Skin Resistance and Their Relationship to G.S.R. Conditioning

Journal of Mental Science ◽

10.1192/bjp.106.442.281 ◽

1960 ◽

Vol 106 (442) ◽

pp. 281-287 ◽

Cited By ~ 18

Author(s):

Irene Martin

Keyword(s):

Action Potentials ◽

Background Activity ◽

Skin Resistance ◽

Muscle Action ◽

Muscle Tonus ◽

Experimental Procedure ◽

Discontinuous Nature ◽

The Subject ◽

Neural Excitation ◽

Set Up

Any particular system which is being conditioned is likely to maintain a certain level of background activity throughout the experimental procedure; either of a discontinuous nature, as, for example, with eyeblink, heart rate and respiratory cycle, or continuously, as in the case of basal skin resistance and muscle tonus. This background activity or level of arousal does not remain constant but usually varies in time, presumably as a result of underlying neural excitation or inhibition. It may increase throughout an experiment if the subject becomes highly motivated, as with the gradients of muscle action potentials observed by Bartoshuk (1955), or decrease, if the subject becomes more relaxed and familiar with the set-up, as Duffy and Lacey (1946) found with level of skin conductance.

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Effects of estrogen on action potential and membrane currents in guinea pig ventricular myocytes

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.277.2.h826 ◽

1999 ◽

Vol 277 (2) ◽

pp. H826-H833 ◽

Cited By ~ 12

Author(s):

Seiko Tanabe ◽

Toshio Hata ◽

Masayasu Hiraoka

Keyword(s):

Guinea Pig ◽

Action Potential ◽

Action Potentials ◽

Voltage Dependence ◽

Ventricular Myocytes ◽

Membrane Currents ◽

Patch Clamp Technique ◽

17Β Estradiol ◽

Electrophysiological Effects ◽

Ionic Basis

To explore a possible ionic basis for the prolonged Q-T interval in women compared with that in men, we investigated the electrophysiological effects of estrogen in isolated guinea pig ventricular myocytes. Action potentials and membrane currents were recorded using the whole cell configuration of the patch-clamp technique. Application of 17β-estradiol (10–30 μM) significantly prolonged the action potential duration (APD) at 20% (APD20) and 90% repolarization (APD90) at stimulation rates of 0.1–2.0 Hz. In the presence of 30 μM 17β-estradiol, APD20 and APD90 at 0.1 Hz were prolonged by 46.2 ± 17.1 and 63.4 ± 11.7% of the control ( n = 5), respectively. In the presence of 30 μM 17β-estradiol the peak inward Ca2+ current ( I CaL) was decreased to 80.1 ± 2.5% of the control ( n = 4) without a shift in its voltage dependence. Application of 30 μM 17β-estradiol decreased the rapidly activating component of the delayed outward K+ current ( I Kr) to 63.4 ± 8% and the slowly activating component ( I Ks) to 65.8 ± 8.7% with respect to the control; the inward rectifier K+ current was barely affected. The results suggest that 17β-estradiol prolonged APD mainly by inhibiting the I Kcomponents I Krand I Ks.

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Long-term observations of spontaneous electrical activity of the uterine smooth muscle

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1959.196.2.343 ◽

1959 ◽

Vol 196 (2) ◽

pp. 343-350 ◽

Cited By ~ 23

Author(s):

C. Y. Kao

Keyword(s):

Smooth Muscle ◽

Electrical Activity ◽

Action Potentials ◽

Local Conditions ◽

Pregnant Uterus ◽

Implanted Electrodes ◽

Spontaneous Electrical Activity ◽

Myometrial Cells ◽

Uterine Smooth Muscle

The spontaneous electrical activity of uterine smooth muscle was rather variable when acute observations were made. Therefore, a series of chronic experiments was performed with implanted electrodes to monitor a group of myometrial cells under different physiological conditions for periods up to eight weeks. The results showed that consistent behavior of myometrial cells could be observed provided similar hormonal status was maintained. Action potentials were rare or absent in myometrium of oophorectomized animals but were caused to appear by estrogen. In the pregnant uterus, action potentials increased both in amplitude and frequency of discharge as parturition approached, reached a peak at that time, and then declined in the postpartum days. The results indicated that in estrogen treatment and in parturition activities of myometrial cells were more synchronous. There was suggestive evidence that there were central impulses initiating activity in the pregnant uterus, and that the responses of the myometrium were affected by the local conditions.

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