[Ca²⁺]_i‐sensitive, IP₃‐independent Ca²⁺ influx in smooth muscle of rat vas deferens revealed by procaine

Abstract

1 The actions of procaine (10 mM) on noradrenaline-induced effects on 45Ca-influx, 45Ca-efflux, 45Ca-content, total inositol phosphates, inositol-1,4,5-trisphosphate, and contractile status of the rat vas deferens were examined.2 Noradrenaline alone had no effect on 45Ca-influx or 45Ca-content, but released Ca2+ from intracellular stores as indicated by an increased 45Ca-efflux and increased total inositol phosphates, specifically inositol-1,4,5-trisphosphate, leading to contraction of the rat vas deferens. 3 Noradrenaline, in the presence of 10 mM procaine, increased 45Ca-influx and 45Ca-content. Procaine blocked the noradrenaline-induced 45Ca-efflux, the increase in total inositol phosphates, the increase in inositol-1,4,5-trisphosphate, and contraction.4 The noradrenaline-induced increase in 45Ca influx which was observed in the presence of procaine was abolished by phentolamine and nifedipine but was not altered significantly by propranolol suggesting that, in the presence of procaine, noradrenaline activates dihydropyridine-sensitive calcium channels through a-adrenoceptors. 5 These findings indicate that, in the rat vas deferens, noradrenaline induces contraction by releasing intracellularly stored Ca2+. The effects of procaine appear to be due to its ability to block the release of Ca2+ from intracellular stores. Furthermore, the simultaneous increase in 45Ca influx and inhibition of inositol-1,4,5-trisphosphate formation in tissues treated with procaine plus noradrenaline indicates that Ca2+ influx is independent of inositol-1,4,5-trisphosphate formation.

Pharmacological Modulation of Sarcoplasmic Reticulum Function in Smooth Muscle

“…Indeed, in intact strips of porcine coronary artery, procaine (1-10 mM) concentration-dependently inhibits and eventually completely suppresses Ach-induced (10 M) production of phosphatidyl inositol 4,5-bisphosphate, a surrogate marker of InsP 3 (Ueno et al, 1987). Likewise, in reserpinized rat vas deferens, procaine (10 mM) prevents NE-induced (10 M) tissue increase in total inositol phosphates and in InsP 3 in particular (Khoyi et al, 1993). Whether this effect is mediated by a direct inhibition of phospholipase C and/or of an upstream event (e.g., by affecting plasma membrane fluidity, see below) is still undetermined.…”

“…Similarly, procaine (10 mM) increases Ca 2ϩ influx induced by NE (10 M) in reserpinized rat vas deferens (Khoyi et al, 1993) and by Cch in guinea pig taenia caeci (Ahn and Karaki, 1988), occurring in both cases through Ca L . This Ca 2ϩ -channel inhibition may be a consequence of procaine membrane stabilizing effect on depolarized plasma membrane that it shares with other local anesthetics, an effect that can be overcome by extracellular Ca 2ϩ (Ahn and Karaki, 1988) but not by activators of Ca L (Ahn and Karaki, 1988).…”

“…However, in reserpinized rat vas deferens, procaine (10 mM) prevents NE-induced increase in Ca 2ϩ efflux (NE ϭ 100 M), increases tissue Ca 2ϩ content (NE ϭ 10 M), and completely inhibits NE-induced (10 M) contractile activity in the absence of extracellular Ca 2ϩ (Khoyi et al, 1993). Similarly, in the absence of extracellular Ca 2ϩ , procaine (1 mM) inhibits Cch-induced (1-1000 M) guinea pig taenia caeci contractile activity (Yagi et al, 1985).…”

“…Molecular structure of procaine (1) and cocaine (2). Ureter Guinea pig Isolated strips; double sucrose-gap; membrane potential, contractile activity 10 mM Burdyga and Magura, 1986 Urinary bladder Guinea pig Isolated strips; microelectrode, isometric dynamometry; membrane potential, contractile activity 10 mM Fujii et al, 1990 Urinary bladder Guinea pig Isolated tissue; single sucrose-gap, microelectrode; membrane potential, contractile activity 1, 7, and 15 mM Kurihara and Sakai, 1976b Urinary bladder Guinea pig Isolated tissue; single sucrose-gap; membrane potential, contractile activity 15 mM Kurihara, 1975 Vas deferens Rat Isolated tissue; 45 Ca 2ϩ cellular loading, ͓ 3 H͔-myoinositol incubated, isometric dynamometry; Ca 2ϩ fluxes, accumulation of inositol phosphates, contractile activity 10 mM Khoyi et al, 1993 Vas deferens Rat Isolated segments; isometric dynamometry; contractile activity 10 mM Huang, 1995Huang, 484 1999. Conversely, the relaxation of ileal longitudinal smooth muscle induced by decreasing [Ca 2ϩ ] is reduced by ruthenium red (100 M) (Yamada et al, 1999).…”

Physiology of the vas deferens

“…The muscular coat consists of inner and outer longitudinal fibers separated by a middle circular layer [ 13,16]. Smooth-muscle cells are closely apposed to each other with gaps as close as 15-20 nm, without nexus-like coupling [13,22]. This close ar-…”