抄録
We previously showed that plasma membrane Ca2+-ATPase (PMCA) activity accounts for ∼25% of relaxation in urinary bladder muscle expressed with PMCA1 and 4 (Li et al. Am J Physiol 290:C1239, 2006). To address the role of these isoforms, we measured [Ca2+]i using FuraPE3 with simultaneous measurements of contractility in the bladder muscle from wild type (WT), Pmca1+/−, Pmca4+/−, Pmca4−/−, and Pmca1+/−Pmca4−/−. Basal [Ca2+]i levels of tested muscles were ∼160 nM without significant difference among genotypes. KCl (80 mM) elicited both larger forces (150-190%) and increases in [Ca2+]i (130-180%) in muscles from Pmca1+/− and Pmca1+/−Pmca4−/− than those in WT and Pmca4−/−. The responses to carbachol (CCh, 0.01 mM) were also greater in Pmca1+/− than in WT muscles. In contrast, CCh-induced responses of force and [Ca2+]i in Pmca4−/−, and Pmca1+/−Pmca4−/− were significantly smaller (40-70%) than in WT. The rise in half-times of force and [Ca2+]i signal in response to KCl and CCh and the half-times of their decay upon washout of stimulant were prolonged in muscles of Pmca4−/− (130-190%) and Pmca1+/−Pmca4−/− (120-250%), but not in Pmca1+/−, with respect to those in WT. Our evidence indicates distinct isoform functions with the PMCA1 isoform involved in overall Ca2+ clearance, while PMCA4 is essenital for the CCh-mediated signal transduction in E-C coupling. HL-66044 (RJP) and HL-61974 (GES and RJP). [J Physiol Sci. 2007;57 Suppl:S67]
