Anomalous response to potassium in vascular smooth muscle cells of human saphenous vein
1 We have examined the relationship between the resting membrane potential (Em) and the concentration of the external ions, K+, Cl− and Ca2+, as well as the effects of K+ on active force generation in human saphenous veins.
2 As measured with sharp glass microelectrodes, the Em 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 m m produced an incremental depolarization, revealing a maximal slope factor of 15 mV per 10-fold increase.
3 Oubain (1.0 m) did not have any effect on Em (−79.0 ± 8.0 mV; n = 80). Replacement of external Cl− with propionate resulted in significant (P < 0.05) depolarization (Em: −65.5 ± 7.5 mV; n = 40). In Cl−-free buffer containing 80 m m K+, Em 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 m m [K+]e and Cl− 138.7 m m. Removal of Ca2+ did not significantly modify the depolarizing response to K+ 80 m m: Em, −68.2 ± 4.9 mV (n = 42) vs.−64.7 ± 6.5 mV (n = 55) in the presence of Ca2+.
4 Despite their small size, changes in Em correlated closely with force generation in buffer containing high K+, approximately 3.62 mN force being generated per mV of change in Em.
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 Em, and (iii) electromechanical coupling has a low threshold.
Document Type: Research Article
Affiliations: 1: Division of Basic Medical Sciences, Faculty of Medicine, Memorial University of Newfoundland, Health Sciences Centre, St John's, NL, A1B 3V6 2: Discipline of Surgery, Health Care Corporation of St. John's, St John's, NL, Canada
Publication date: January 1, 2006