APStracts 3:0300H, 1996.

Alpha-adrenoceptor activation of a chloride conductance in rat iris arterioles. Gould, Dianna J., and Caryl E. Hill. Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia

APStracts 3:0300H, 1996.

Changes in membrane potential associated with [alpha]-adrenoceptor mediated contraction of rat iris arterioles following nerve stimulation (10 Hz, 1 s) have been measured using conventional intracellular recording techniques. Two different types of intracellular responses were recorded. Cells showing a depolarisation are proposed to represent the arteriolar smooth muscle cells since the characteristics of the depolarisation are correlated with those of the contraction. Cells which show no response or a small hyperpolarisation in response to nerve stimulation are proposed to represent the endothelial cells of the arteriole. Both the depolarisation and the contraction were abolished by tetrodotoxin (1 [mu]M), benextramine (10 [mu]M) and prazosin (0.1 mM) indicating that they result from nerve-mediated activation of [alpha]-adrenoceptors. A small but significant part of the contraction (30%) and the depolarisation (11%) was nifedipine-sensitive (10 [mu]M). Caffeine (1mM) abolished the contraction and reduced the depolarisation by half. Reducing the external chloride concentration also abolished the contraction and reduced the depolarisation by 90%. Flufenamic acid (250 mM) abolished both the contraction and the depolarisation. It is suggested that, in iris arterioles, the activation of synaptic [alpha]-adrenoceptors leads to the release of intracellular calcium which activates both chloride channels in the cell membrane leading to depolarisation, and the intracellular contractile apparatus leading to vasoconstriction.

Received 20 February 1996; accepted in final form 27 June 1996.
APS Manuscript Number H163-6.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996