Physiological Features of Visceral Smooth Muscle Cells, With Special Reference to Receptors and Ion Channels

Abstract

Visceral smooth muscle cells (VSMC) play an essential role, through changes in their contraction-relaxation cycle, in the maintenance of homeostasis in biological systems. The features of these cells differ markedly by tissue and by species; moreover, there are often regional differences within a given tissue. The biophysical features used to investigate ion channels in VSMC have progressed from the original extracellular recording methods (large electrode, single or double sucrose gap methods), to the intracellular (microelectrode) recording method, and then to methods for recording from membrane fractions (patch-clamp, including cell-attached patch-clamp, methods). Remarkable advances are now being made thanks to the application of these more modern biophysical procedures and to the development of techniques in molecular biology. Even so, we still have much to learn about the physiological features of these channels and about their contribution to the activity of both cell and tissue. In this review, we take a detailed look at ion channels in VSMC and at receptor-operated ion channels in particular; we look at their interaction with the contraction-relaxation cycle in individual VSMC and especially at the way in which their activity is related to Ca2+ movements and Ca2+ homeostasis in the cell. In sections II and III, we discuss research findings mainly derived from the use of the microelectrode, although we also introduce work done using the patch-clamp procedure. These sections cover work on the electrical activity of VSMC membranes (sect. II) and on neuromuscular transmission (sect. III). In sections IV and V, we discuss work done, using the patch-clamp procedure, on individual ion channels (Na+, Ca2+, K+, and Cl-; sect. IV) and on various types of receptor-operated ion channels (with or without coupled GTP-binding proteins and voltage dependent and independent; sect. V). In sect. VI, we look at work done on the role of Ca2+ in VSMC using the patch-clamp procedure, biochemical procedures, measurements of Ca2+ transients, and Ca2+ sensitivity of contractile proteins of VSMC. We discuss the way in which Ca2+ mobilization occurs after membrane activation (Ca2+ influx and efflux through the surface membrane, Ca2+ release from and uptake into the sarcoplasmic reticulum, and dynamic changes in Ca2+ within the cytosol). In this article, we make only limited reference to vascular smooth muscle research, since we reviewed the features of ion channels in vascular tissues only recently.

Novel type of interstitial cell (Cajal-like) in human fallopian tube

“…48). The potentials were rather short (0.98 + 0.07 ms) when compared to the electrophysiological properties of smooth muscle cells [88]. These preliminary results show that t-ICC in subconfluent primary culture have spontaneous electrical activity.…”

Properties of Unitary Potentials Recorded from Myenteric Interstitial Cells of Cajal Distributed in the Guinea-Pig Gastric Antrum

“…Papaverine is known to increase intracellular cAMP levels due to nonselective inhibition of the activity of phosphodiesterases (Berndt et al, 1976). In several types of smooth muscle tissues, cAMP decreases [Ca 2+ ]i through activation of protein kinase A (PKA; Kuriyama et al, 1998). These results suggest that in ICC-MY, the generation of unitary potentials requires an elevation of [Ca 2+ ]i, as in the case of unitary potentials generated in ICC-IM (Edwards et al, 1999).…”

“…Therefore, experiments were carried out to investigate the effects of BAPTA-AM (an internal Ca 2+ chelator) and papaverine (a non selective phosphodiesterase inhibitor) on unitary potentials, since both of these chemicals are considered to reduce intracellular Ca 2+ concentration (Kuriyama et al, 1998), but through different mechanisms, in gastric smooth muscles.…”

Effects of Dai-kenchu-to on spontaneous activity in the mouse small intestine

“…5), indicating that at least cholinergic and nitrergic nerves distribute on mouse small intestine. In general ACh contracts and NO relaxes gastrointestinal smooth muscle cells (Kuriyama et al, 1998). It is interesting that DKT produce two opposing effects (cholinergic excitatory and nitrergic inhibitory) on intestinal motility.…”