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Distinct roles of PMCA isoforms in Ca2+ homeostasis of bladder smooth muscle: evidence from PMCA gene-ablated mice
Li Liu1, Yukisato Ishida, Gbolahan Okunade
1Molecular and Cellular Physiology, University of Cincinnati College of Medicine, 231 Albert Sabin Way, Cincinnati, OH 45267-0576, USA.
Abstract:
We previously showed that plasma membrane Ca(2+)-ATPase (PMCA) activity accounted for 25-30% of relaxation in bladder smooth muscle (8). Among the four PMCA isoforms only PMCA1 and PMCA4 are expressed in smooth muscle. To address the role of these isoforms, we measured cytosolic Ca(2+) ([Ca(2+)](i)) using fura-PE3 and simultaneously measured contractility in bladder smooth muscle from wild-type (WT), Pmca1(+/-), Pmca4(+/-), Pmca4(-/-), and Pmca1(+/-)Pmca4(-/-) mice. There were no differences in basal [Ca(2+)](i) values between bladder preparations. KCl (80 mM) elicited both larger forces (150-190%) and increases in [Ca(2+)](i) (130-180%) in smooth muscle from Pmca1(+/-) and Pmca1(+/-)Pmca4(-/-) bladders than those in WT or Pmca4(-/-). The responses to carbachol (CCh: 10 muM) were also greater in Pmca1(+/-) (120-150%) than in WT bladders. In contrast, the responses in Pmca4(-/-) and Pmca1(+/-)Pmca4(-/-) bladders to CCh were significantly smaller (40-50%) than WT. The rise in half-times of force and [Ca(2+)](i) increases in response to KCl and CCh, and the concomitant half-times of their decrease upon washout of agonist were prolonged in Pmca4(-/-) (130-190%) and Pmca1(+/-)Pmca4(-/-) (120-250%) bladders, but not in Pmca1(+/-) bladders with respect to WT. Our evidence indicates distinct isoform functions with the PMCA1 isoform involved in overall Ca(2+) clearance, while PMCA4 is essential for the [Ca(2+)](i) increase and contractile response to the CCh receptor-mediated signal transduction pathway.
Insights
Plasma membrane Ca(2+)-ATPase (PMCA) isoform 1 aids bladder smooth muscle relaxation, while PMCA4 is crucial for carbachol-induced contractions. This study clarifies distinct PMCA roles in bladder function.
Area of Science:
- Physiology
- Molecular Biology
- Urology
Background:
- Plasma membrane Ca(2+)-ATPase (PMCA) activity contributes significantly to bladder smooth muscle relaxation.
- Four PMCA isoforms exist, with PMCA1 and PMCA4 identified in smooth muscle.
Purpose of the Study:
- To investigate the distinct roles of PMCA1 and PMCA4 isoforms in bladder smooth muscle contractility and Ca(2+) handling.
- To elucidate the functional differences between PMCA1 and PMCA4 in response to various stimuli.
Main Methods:
- Measurements of cytosolic Ca(2+) ([Ca(2+)](i)) using fura-PE3 in bladder smooth muscle.
- Simultaneous measurement of contractility in bladder smooth muscle from wild-type (WT), Pmca1(+/-), Pmca4(-/-), and compound mutant mice.
- Stimulation with KCl and carbachol (CCh) to assess muscle responses.
Main Results:
- Bladder smooth muscle from Pmca1(+/-) and Pmca1(+/-)Pmca4(-/-) mice exhibited significantly larger forces and [Ca(2+)](i) increases in response to KCl compared to WT or Pmca4(-/-) mice.
- Responses to carbachol (CCh) were enhanced in Pmca1(+/-) bladders but significantly reduced in Pmca4(-/-) and Pmca1(+/-)Pmca4(-/-) bladders.
- The decay of force and [Ca(2+)](i) after CCh washout was prolonged in Pmca4(-/-) and compound mutant bladders, indicating impaired Ca(2+) clearance.
Conclusions:
- PMCA1 isoform is primarily involved in the overall clearance of Ca(2+) in bladder smooth muscle.
- PMCA4 isoform plays a critical role in mediating the cytosolic Ca(2+) increase and contractile response to carbachol-mediated signaling.
- Distinct functional roles of PMCA isoforms are essential for regulating bladder smooth muscle activity.
