Effects of reserpine on tissue calcium and contractility of rat and rabbit aorta

Possible effects of reserpine on disposition and availability of tissue calcium, stores for excitation-contraction coupling in isolated rat and rabbit aortae were examined. Contral 40Ca uptake, 45Ca washout, and contraction in Ca2+-free medium (Ca2+-free PSS) indicate species differences in binding or disposition, apparent functional importance, and differential use of tissue calcium by adrenaline (Epi) and high K+. Rat aortae, normally refractory to Epi or high K+ after 7 min in Ca2+-free PSS, can gain labile calcium after brief exposure to Ca2+-rich PSS which supports short-lived responses to high K+ in Ca2+-free PSS. Rabbit aortae contain calcium stores which may sustain either Epi or high-K+ responses as well as more tightly held (or sequestered) stores released by Epi for contraction. After reserpine, decreased 45Ca uptake in a kinetically defined "fast" compartment likely to include membrane calcium could enhance availability of bound tissue as well as free Ca2+ in both species. Enhanced Epi response in Ca2+-free PSS is evidence of the former. Results suggest that increased availability of bound and possibly free calcium contribute to reserpine-induced supersensitivity, but supporting evidence will be required from tissue behavior after less rigorous treatment.