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

Abstract

Possible effects of reserpine on disposition and availability of tissue calcium stores for excitation–contraction coupling in isolated rat and rabbit aortae were examined. Control 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.