Voltage-dependent anion-selective channels in cultured smooth muscle cells of the rat aorta

Electrical and pharmacological properties of the single Ca-activated K channel in cultured smooth muscle cells (SMC) of the rat aorta were studied with the patch-clamp technique. The Ca-activated K channel had a slope conductance (gamma K) of 135 +/- 2 pS (mean +/- SE; n = 5) in symmetrical 142 mM K solutions. The reversal potentials show a 56-mV change for a 10-fold change in the external K concentration. Probability of the channel opening increased when the intracellular Ca concentration ([Ca]i) was increased over 10(-7) M or the membrane was depolarized. The channel was blocked by either external tetraethylammonium (TEA, 10–30 mM) or by internal Ba (1–5 mM). Channel activities were characterized by burst-like openings. Open-time histogram was fitted with a single exponential (tau = 1.3 ms at +10 mV and 10(-7) M [Ca]i), whereas the closed-time histogram was fitted with two exponentials (tau 1 = 0.7 ms and tau 2 = 111 ms). The permeability ratio for monovalent cations calculated with the Goldman-Hodgkin-Katz equation was K:Rb:Na = 1:0.7: less than 0.01. We conclude from these observations that the Ca-activated K channel in cultured SMC of the rat aorta is characterized by a middle size gamma K, activation by [Ca]i increase and depolarization, relatively low sensitivity to TEA, and high selectivity for K ions.

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Cyclic AMP modulates Ca-activated K channel in cultured smooth muscle cells of rat aortas

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1988.255.4.h754 ◽

1988 ◽

Vol 255 (4) ◽

pp. H754-H759 ◽

Cited By ~ 10

Author(s):

J. Sadoshima ◽

N. Akaike ◽

H. Kanaide ◽

M. Nakamura

Keyword(s):

Smooth Muscle ◽

Smooth Muscle Cells ◽

Muscle Cells ◽

Rat Aorta ◽

K Channel ◽

Free Calcium ◽

Bathing Solution ◽

Patch Clamp Technique ◽

K Channels ◽

Cultured Smooth Muscle Cells

Effects of adenosine 3',5'-cyclic monophosphate (cAMP) on single Ca-activated K current (IK(Ca)) in cultured smooth muscle cells of the rat aorta were investigated with the patch-clamp technique. In cell-attached patch configurations, extracellular application of isoproterenol (10(-5) M) increased the Ca-activated K currents. The increase in the currents was due to an increase in the probability of channel openings (Po). Neither unit conductance nor the maximum number of the channel in the patch was affected by the drug. The effects were inhibited by adding propranolol (10(-6) M). The extracellular application of forskolin (10(-5) M) or dibutyryl cAMP (10(-4) M) mimicked the effects of isoproterenol. In inside-out patch configurations, activated cAMP-dependent protein kinase (A kinase) in the bathing solution increased the sensitivity of the Ca-activated K channels to intracellular free calcium concentration ([Ca]i) and enhanced Po. Kinetic analyses of the IK(Ca) showed that cAMP-dependent phosphorylation of the Ca-activated K channels significantly reduced the mean closed time between bursting openings. We conclude from these observations that the Ca-activated K channels in aortic cells may increase Po through cAMP-dependent phosphorylation.

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