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.
Bieger
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Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, Health Sciences Centre, St John's, NL, Canada A1B 3V6.
Mong
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Tabrizchi
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D000368:Aged; D002021:Buffers; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000502:physiology; D011188:Potassium / Q000494:pharmacology*; D012501:Saphenous Vein / Q000187:drug effects* / Q000502:physiology
D002021:Buffers; D002712:Chlorides; D011188:Potassium