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

Authors: Bieger, D.¹; Mong, K.²; Tabrizchi, R.¹

Source: Autonomic & Autacoid Pharmacology, Volume 26, Number 1, January 2006 , pp. 1-6(6)

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Abstract:

Summary

1 We have examined the relationship between the resting membrane potential (E_m) 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 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 m m produced an incremental depolarization, revealing a maximal slope factor of 15 mV per 10-fold increase.

3 Oubain (1.0 μ m) 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 m m 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 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: E_m, −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 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.

Keywords: human vascular smooth muscle; membrane potential; excitation–contraction coupling; potassium; chloride

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1474-8673.2005.00351.x

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: 2006-01-01

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

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