159: Deletion of SM-B, the High Atpase Isoform of Myosin, Upregulates the PKC-Mediated Signal Transduction Pathway in the Urinary Bladder Smooth Muscle

We previously showed that plasma membrane Ca2+-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 Ca2+ ([Ca2+]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 [Ca2+]i values between bladder preparations. KCl (80 mM) elicited both larger forces (150–190%) and increases in [Ca2+]i (130–180%) in smooth muscle from Pmca1+/− and Pmca1+/− Pmca4−/− bladders than those in WT or Pmca4−/−. The responses to carbachol (CCh: 10 μM) 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 [Ca2+]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 Ca2+ clearance, while PMCA4 is essential for the [Ca2+]i increase and contractile response to the CCh receptor-mediated signal transduction pathway.

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Deletion of SM-B, the high ATPase isoform of myosin, upregulates the PKC-mediated signal transduction pathway in murine urinary bladder smooth muscle

AJP Renal Physiology ◽

10.1152/ajprenal.90221.2008 ◽

2009 ◽

Vol 296 (3) ◽

pp. F658-F665 ◽

Cited By ~ 8

Author(s):

Joseph A. Hypolite ◽

Shaohua Chang ◽

Edward LaBelle ◽

Gopal J. Babu ◽

Muthu Periasamy ◽

...

Keyword(s):

Signal Transduction ◽

Smooth Muscle ◽

Rabbit Model ◽

Outlet Obstruction ◽

Signal Transduction Pathway ◽

Transduction Pathway ◽

Bladder Smooth Muscle ◽

Two Dimensional Gel Electrophoresis ◽

Compensatory Response ◽

Myosin Heavy Chain Isoform

Detrusor smooth muscle (DSM) hypertrophy induced by partial bladder outlet obstruction (PBOO) is associated with changes in the NH2-terminal myosin heavy chain isoform from predominantly SM-B to SM-A, alteration in the Ca2+ sensitization pathway, and the contractile characteristics from phasic to tonic in rabbits. We utilized the SM-B knockout (KO) mouse to determine whether a shift from SM-B to SM-A without PBOO is associated with changes in the signal transduction pathway mediated via PKC and CPI-17, which keeps the myosin phosphorylation (MLC20) level high by inhibiting the myosin phosphatase. DSM strips from SM-B KO mice generated more force in response to electrical field stimulation, KCl, carbachol, and phorbol 12,13-dibutyrate than that of age-matched wild-type mice. There was no difference in the ED50 for carbachol but the maximum response was greater for the SM-B KO mice. DSM from SM-B KO mice revealed increased mass and hypertrophy. The KO mice also showed an overexpression of PKC-α, increased levels of phospho-CPI-17, and an elevated level of IP3 and DAG upon stimulation with carbachol. Two-dimensional gel electrophoresis revealed an increased level of MLC20 phosphorylation in response to carbachol. Together, these changes may be responsible for the higher level of force generation and maintenance by the DSM from the SM-B KO bladders. In conclusion, our data show that ablation of SM-B is associated with alteration of PKC-mediated signal transduction and CPI-17-mediated Ca2+ sensitization pathway that regulate smooth muscle contraction. Interestingly, similar changes are also present in PBOO-induced DSM compensatory response in the rabbit model in which SM-B is downregulated.

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Evidence that action potential generation is not the exclusive determinant to trigger spontaneous myogenic contraction of guinea-pig urinary bladder smooth muscle

Acta Physiologica Scandinavica ◽

10.1046/j.1365-201x.2002.01009.x ◽

2002 ◽

Vol 176 (1) ◽

pp. 57-63 ◽

Cited By ~ 4

Author(s):

T. Imai ◽

Y. Tanaka ◽

T. Okamoto ◽

Y. Yamamoto ◽

T. Horinouchi ◽

...

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Guinea Pig ◽

Action Potential ◽

Action Potential Generation ◽

Potential Generation ◽

Bladder Smooth Muscle ◽

Urinary Bladder Smooth Muscle

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Stretch-induced Calcium Release in Smooth Muscle

The Journal of General Physiology ◽

10.1085/jgp.20028514 ◽

2002 ◽

Vol 119 (6) ◽

pp. 533-543 ◽

Cited By ~ 76

Author(s):

Guangju Ji ◽

Robert J. Barsotti ◽

Morris E. Feldman ◽

Michael I. Kotlikoff

Keyword(s):

Smooth Muscle ◽

Urinary Bladder ◽

Smooth Muscle Cells ◽

Calcium Release ◽

Muscle Cells ◽

Intraluminal Pressure ◽

Bladder Smooth Muscle ◽

Urinary Bladder Smooth Muscle ◽

Inward Currents ◽

Longitudinal Stretch

Smooth muscle cells undergo substantial increases in length, passively stretching during increases in intraluminal pressure in vessels and hollow organs. Active contractile responses to counteract increased transmural pressure were first described almost a century ago (Bayliss, 1902) and several mechanisms have been advanced to explain this phenomenon. We report here that elongation of smooth muscle cells results in ryanodine receptor–mediated Ca2+ release in individual myocytes. Mechanical elongation of isolated, single urinary bladder myocytes to ∼120% of slack length (ΔL = 20) evoked Ca2+ release from intracellular stores in the form of single Ca2+ sparks and propagated Ca2+ waves. Ca2+ release was not due to calcium-induced calcium release, as release was observed in Ca2+-free extracellular solution and when free Ca2+ ions in the cytosol were strongly buffered to prevent increases in [Ca2+]i. Stretch-induced calcium release (SICR) was not affected by inhibition of InsP3R-mediated Ca2+ release, but was completely blocked by ryanodine. Release occurred in the absence of previously reported stretch-activated currents; however, SICR evoked calcium-activated chloride currents in the form of transient inward currents, suggesting a regulatory mechanism for the generation of spontaneous currents in smooth muscle. SICR was also observed in individual myocytes during stretch of intact urinary bladder smooth muscle segments. Thus, longitudinal stretch of smooth muscle cells induces Ca2+ release through gating of RYR. SICR may be an important component of the physiological response to increases in luminal pressure in smooth muscle tissues.

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