Distinct effects of CGRP on typical and atypical smooth muscle cells involved in generating spontaneous contractions in the mouse renal pelvis

Abstract

Background and purpose: We investigated the cellular mechanisms underlying spontaneous contractions in the mouse renal pelvis, regulated by calcitonin gene-related peptide (CGRP). Experimental approach: Spontaneous contractions, action potentials and Ca 2+ transients in typical and atypical smooth muscle cells (TSMCs and ATSMCs) within the renal pelvis wall were recorded separately using tension and intracellular microelectrode recording techniques and Fluo-4 Ca 2+ imaging. Immunohistochemical and electron microscopic studies were also carried out. Key results: Bundles of CGRP containing transient receptor potential cation channel, subfamily V, member 1-positive sensory nerves were situated near both TSMCs and ATSMCs. Nerve stimulation reduced the frequency but augmented the amplitude and duration of spontaneous phasic contractions, action potentials and Ca 2+ transients in TSMCs. CGRP and agents increasing internal cyclic adenosine monophosphate (cAMP) mimicked the nerve-mediated modulation of TSMC activity and suppressed ATSMCs Ca 2+ transients. Membrane hyperpolarization induced by CGRP or cAMP stimulators was blocked by glibenclamide, while their negative chronotropic effects were less affected. Glibenclamide enhanced TSMC Ca 2+ transients but inhibited ATSMC Ca 2+ transients, while both 5-hydroxydecanoate and diazoxide, a blocker and opener of mitochondrial ATP-sensitive K + channels, respectively, reduced the Ca 2+ transient frequency in both TSMCs and ATSMCs. Inhibition of mitochondrial function blocked ATSMCs Ca 2+ transients and inhibited spontaneous excitation of TSMCs. Conclusions and implications: The negative chronotropic effects of CGRP result primarily from suppression of ATSMC Ca 2+ transients rather than opening of plasmalemmal ATP-sensitive K + channels in TSMCs. The positive inotropic effects of CGRP may derive from activation of TSMC L-type Ca 2+ channels. Mitochondrial Ca 2+ handling in ATSMCs also plays a critical role in generating Ca 2+ transients. © 2009 The British Pharmacological Society All rights reserved.