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

Influence of tangential stress on mechanical responses to vasoactive agents in human saphenous vein with and without perivascular adipose tissue

AIM

Improvement in short-term patency of vein grafts harvested with the surrounding tissue and no distention has been noted. The influence of transient tangential stress on mechanical function to vasoactive agents in isolated human saphenous veins stripped or with attached perivascular adipose tissue was assessed.

METHODS

Concentration-response curves to noradrenaline, 5-hydroxytryptamine, methylcholine, sodium nitroprusside and nicardipine were constructed for veins exposed to no, low (approximately 120 mmHg) or high (approximately 240 mmHg) tangential stress.

RESULTS

Tangential stress did not affect contractile effects of noradrenaline or relaxant effects of methylcholine and sodium nitroprusside. Regression analysis of the concentration-response curve to 5-hydroxytryptamine revealed a significant (P=0.042) increase in sensitivity in saphenous veins without perivascular adipose tissue exposed to no tangential stress, compared with veins with attached adipose tissue. Exposure to high stress significantly (P=0.024) increased the potency of 5-hydroxytryptamine in blood vessels without perivascular adipose tissue, as opposed to veins with adipose tissue. Relaxant responses to nicardipine in veins with perivascular adipose tissue were significantly (P=0.001) affected by exposure to low tangential stress compared with no or high tangential stress. A parallel comparison revealed that intact veins compared with those without perivascular adipose tissue exposed to low stress were significantly (P=0.020) more resistant to the relaxant effects of nicardipine.

CONCLUSION

The findings of the present report support the view that tangential stress has an impact on the actions of vasoactive agents, but this influence is variable and factor(s) released from perivascular adipose tissue may have a bearing on the observed effect.

Relaxant responses to calcium channel antagonists and potassium channel opener in human saphenous vein

1.-- As shown in a parallel study the magnitude of depolarization induced in human saphenous vein by raising external potassium ([K(+)](e)) falls markedly below the theoretical values predicted by the Goldman-Hodgkin-Katz equations. This anomaly prompted us to re-examine the relaxant actions of L-type (nifedipine) and T-type (mibefradil) Ca(2+) channel antagonists, and relaxant and electrophysiological effects of the K(+) channel opener, pinacidil, on saphenous veins contracted by the elevation of [K(+)](e). 2.-- Nifedipine produced concentration-dependent relaxations in tissues contracted at various high [K(+)](e). In tissues contracted with 20 mm [K(+)](e), the pIC(50) for nifedipine was significantly (8.20 +/- 0.05; n = 6; mean +/- SEM; P < 0.05) greater than in tissues contracted with > or =40 mm [K(+)](e). 3.-- Tissues contracted with 20 mm [K(+)](e) also relaxed in response to mibefradil (pIC(50) = 6.1 +/- 0.14) and pinacidil (pIC(50) = 6.45 +/- 0.08), the latter being almost completely reversed (93.4 +/- 9.9%) by addition of glibenclamide (10 microm). 4.-- The resting E(m) of smooth muscle cells of saphenous vein was -77.0 +/- 0.7 mV (n = 52), and 20 mm [K(+)](e) produced a modest but significant depolarization to -73.0 +/- 0.7 mV (n = 52). Incubation with pinacidil plus 20 mm [K(+)](e) resulted in a significant hyperpolarization of the E(m) to -82 +/- 0.6 mV (n = 52). 5.-- N(omega)-nitro-L-arginine methyl ester did not impede the relaxant responses of nifedipine, mibefradil or pinacidil. 6.-- In conclusion, the relaxant effects of nifedipine and pinacidil (i) occurred at an E(m) distinctly below the presumed threshold for the opening of the classic (Ca(V)1.3alpha(1)) L-type Ca(2+) channels, and (ii) did not depend on generation of nitric oxide.