Role of plasma membrane Ca²⁺-ATPase (PMCA) in contraction-relaxation processes of the bladder using PMCA gene manipulation

Abstract

Role of PMCA in smooth muscle contractility was investigated using the bladder isolated from PMCA gene manipulated mice: PMCA4 null mutant (Pmca4^−/−) and PMCA1 and PMCA4 double gene targeted (Pmca1^+/−4^−/−) mice. Western blot shows the loss of PMCA4, a major isoform, but not PMCA1, sarco-endoplasmic reticulum ATPase (SERCA) and Na⁺/Ca²⁺ exchanger (NCX), in the muscle layer preparation of Pmca4^−/− and Pmca1^+/−4^−/−. Half-times of contraction and relaxation upon treatment with 80 mM KCl were determined. Surprisingly, half-times of contraction in Pmca4^−/− and Pmca1^+/−4^−/− muscles tended to be prolonged, when compared with that in WT muscle. Relaxation half-times were also prolonged in the gene manipulated muscles, as expected. On the other hand, inhibition of SERCA or NCX marginally shortened the contraction half-time and prolonged the relaxation half-time in muscles of all tested genotypes. Using relaxation half times, the contribution of PMCA to relaxation was calculated to be 25%, SERCA 20% and NCX 70%. PMCA and SERCA appeared to function additively, but the function of NCX might overlap with those of other components. FuraPE3 signal shows that the basal level of [Ca²⁺]i slightly increased in Pmca1^+/−4^−/− muscle. In summary, the gene manipulation of PMCA indicates that PMCA, in addition to SERCA and NCX plays a role in both excitation-contraction coupling and Ca²⁺-extrusion-relaxation relationship, i.e., Ca²⁺ homeostasis, of the bladder smooth muscle. [J Physiol Sci. 2006;56 Suppl:S69]