Noradrenaline modulation of calcium channels in single smooth muscle cells from rabbit ear artery.

Abstract

1. Whole‐cell recordings of voltage‐gated Ca2+ current in single smooth muscle cells from rabbit ear artery were obtained with 110 mM‐Ba2+ as charge carrier. 2. Noradrenaline (NA, 1‐20 microM) produced a sustained increase in the dihydropyridine‐sensitive L‐type Ca2+ current, ranging up to 3‐fold in some cells. The dihydropyridine‐resistant T‐type Ca2+ current was not affected. 3. The time and voltage dependence of activation and inactivation of the L‐type current were not significantly changed during NA modulation. 4. The NA‐induced increase in L‐current was enhanced in magnitude and consistency by the inclusion of 200 microM‐GTP in the pipette (internal) solution. 5. The effect of NA on L‐current was not abolished by pre‐treatment with prazosin, phentolamine or propranolol, suggesting that it is not mediated by alpha‐ or beta‐adrenoceptors. 6. Phenylephrine (5 microM) was ineffective as an agonist, while adrenaline was approximately equipotent to NA. In these respects, the pharmacology of L‐current modulation resembles that of ‘gamma’‐adrenergic receptors (Hirst & Nield, 1980). 7. NA modulation of L‐type Ca2+ channels may be particularly important in promoting sympathetic vasoconstriction in resistance vessels where Ca2+ stores are relatively poorly developed and where NA‐evoked contractions are very sensitive to organic Ca2+ channel antagonists. © 1988 The Physiological Society