ISSN:
1432-1424
Keywords:
Smooth muscle
;
Glyburide
;
Pinacidil
;
Chloride channels
;
Membrane potential
;
Vasodilation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract We describe the activation of a K+ current and inhibition of a Cl− current by a cyanoguanidine activator of ATP-sensitive K+ channels (KATP) in the smooth muscle cell line A10. The efficacy of U83757, an analogue of pinacidil, as an activator of KATP was confirmed in single channel experiments on isolated ventricular myocytes. The effects of U83757 were examined in the clonal smooth muscle cell line A10 using voltage-sensitive dyes and digital fluorescent imaging techniques. Exposure of A10 cells to U83757 (10 nm to 1 μm) produced a rapid membrane hyperpolarization as monitored by the membrane potential-sensitive dye bis-oxonol ([diBAC4(3)], 5 μm). The U83757induced hyperpolarization was antagonized by glyburide and tetrapropylammonium (TPrA) but not by tetraethlylammonium (TEA) or charybdotoxin (ChTX). The molecular basis of the observed hyperpolarization was studied in whole-cell, voltage-clamp experiments. Exposure of voltage-clamped cells to U83757 (300 nm to 300 μm) produced a hyperpolarizing shift in the zero current potential; however, the hyperpolarizing shift in reversal potential was associated with either an increase or decrease in membrane conductance. In solutions where E k=−82 mV and E Cl=0 mV, the reversal potential of the U83757-sensitive current was approximately −70 mV in those experiments where an increase in membrane conductance was observed. In experiments in which a decrease in conductance was observed, the reversal potential of the U83757-sensitive current was approximately 0 mV, suggesting that U83757 might be acting as a Cl− channel blocker as well as a K+ channel opener. In experiments in which Cl− current activation was specifically brought about by cellular swelling and performed in solutions where Cl− was the major permeant ion, U83757 (300 nm to 300 μm) produced a dose-dependent current inhibition. Taken together these results (i) demonstrate the presence of a K+-selective current which is sensitive to KATP channel openers in A10 cells and (ii) indicate that the hyperpolarizing effects of K+ channel openers in vascular smooth muscle may be due to both the inhibition of Cl− currents as well as the activation of a K+-selective current.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00234998
