A glibenclamide sensitive potassium conductance in terminal arterioles isolated from guinea pig heart.

OBJECTIVE

The aim was to isolate terminal arterioles from guinea pig heart, to describe their basic electrical properties, and to obtain evidence for the presence of KATP channels in microvascular coronary smooth muscle cells.

METHODS

Terminal arterioles of 20-50 microns diameter were obtained by enzymatic digestion of isolated perfused hearts. The isolated arterioles were viable for up to 8 h and constricted upon application of high potassium solution. Whole cell clamp experiments on smooth muscle cells of these arterioles were performed at room temperature.

RESULTS

The resting potential of coronary smooth muscle cells in terminal arterioles showed a bimodal distribution with one peak at -23(SD 8) mV and the other peak at -61(4) mV. Application of glibenclamide (50 microM) to the latter group of arterioles produced a depolarisation to -37(8) mV; application of cromakalim (1 microM) produced a hyperpolarisation to -71(1) mV. The current changes associated with voltage steps and slow voltage ramps in the range -120 to +40 mV indicated that the smooth muscle cells in the arterioles were coupled electrically. The steady state current-voltage relation was sigmoid with a flat region in the range -50 to -30 mV. In the presence of 2-50 microM glibenclamide the slope resistance at potentials negative to -50 mV and positive to -30 mV was markedly increased. In the presence of 1 microM cromakalim the slope resistance was decreased and the current-voltage relation at negative potentials became nearly linear. The crossover point of the current-voltage relations measured under control conditions and in the presence of glibenclamide was near the calculated potassium equilibrium potential.

CONCLUSIONS

Glibenclamide closes and cromakalim opens potassium channels in smooth muscle cells of coronary arterioles. The voltage dependence of the steady state current changes suggests that the current activated by cromakalim is not carried by the same channels as the current inhibited by glibenclamide. The glibenclamide sensitive channels make a significant contribution to the membrane potential of isolated arterioles.