Anomalous response to potassium in vascular smooth muscle cells of human saphenous vein.

1.--We have examined the relationship between the resting membrane potential (E(m)) and the concentration of the external ions, K(+), Cl(-) and Ca(2+), as well as the effects of K(+) on active force generation in human saphenous veins. 2.--As measured with sharp glass microelectrodes, the E(m) of vascular muscle cells was -76.0 +/- 7.0 mV (mean +/- SD; n = 328). Raising the concentration of external potassium ([K(+)](e)) from 4.2 to 20, 40, 80, 120 or 150 mm produced an incremental depolarization, revealing a maximal slope factor of 15 mV per 10-fold increase. 3.--Oubain (1.0 microm) did not have any effect on E(m) (-79.0 +/- 8.0 mV; n = 80). Replacement of external Cl(-) with propionate resulted in significant (P < 0.05) depolarization (E(m): -65.5 +/- 7.5 mV; n = 40). In Cl(-)-free buffer containing 80 mm K(+), E(m) depolarized to -52.0 +/- 6.7 mV (n = 45) compared with -64.7 +/- 6.5 mV (n = 55) (P < 0.05) measured in buffer containing 80 mm [K(+)](e) and Cl(-) 138.7 mm. Removal of Ca(2+) did not significantly modify the depolarizing response to K(+) 80 mm: E(m), -68.2 +/- 4.9 mV (n = 42) vs.-64.7 +/- 6.5 mV (n = 55) in the presence of Ca(2+). 4.--Despite their small size, changes in E(m) correlated closely with force generation in buffer containing high K(+), approximately 3.62 mN force being generated per mV of change in E(m). 5.--These data demonstrate that, in human saphenous smooth muscle cells, (i) the magnitude of depolarization induced by raising [K(+)](e) deviates considerably from the theoretical values predicted by the Goldman-Hodgkin-Katz equations, (ii) Cl(-) appears to contribute to the maintenance of E(m), and (iii) electromechanical coupling has a low threshold.