Variable potency of nitrergic‐nitrovasodilator relaxations of the mouse anococcygeus against different forms of induced tone

Abstract

during Ca2' re-loading, increased the subsequent residual contraction to carbachol in Ca2+-free medium.7 At higher concentrations, SNP (0.1-10 fM) produced a partial relaxation of the sustained contraction to U46619 in Ca2+-free medium. 8 Thus, the relaxant potency of the nitrergic stimuli was dependent on the agent and mechanism used to induce tone in the preparation. Examination of the contractile/relaxant interactions suggests that altered Ca2+ sequestration and inhibition of contractile protein function may underlie nitrergic relaxations of this tissue.

Two distinct membrane currents activated by cyclopiazonic acid‐induced calcium store depletion in single smooth muscle cells of the mouse anococcygeus

“…We have previously shown that CPA-induced contractions of the whole muscle, whilst being largely unaffected by nifedipine (1 giM), are inhibited by SKF 96365, (pIC50 approximately 6.4; Gibson et al, 1994). In the present series of experiments, we extended these observations by testing the ability of several divalent and trivalent cations to inhibit the CPA-induced contractions.…”

“…Second the current was blocked by the chloride channel blockers, DIDS and A-9-C, both of which have been shown to block calcium-dependent chloride currents in other smooth muscles (Baron et al, 1991;Wang et al, 1992). Third, the current-voltage relationship for the current showed marked outward rectification similar to that of the calcium-dependent chloride current first described in smooth muscle cells isolated from the rat anococcygeus (Byrne & Large, 1987 (Gibson et al, 1994).…”

“…The muscles were incubated for 10 min at 370C in a physiological salt solution (PSS) containing zero added calcium plus, in mM: NaCl 120, KCl 6, MgCl2 1.2, Na2HPO4 1.2, glucose 11, HEPES 10, pH 7.2. Following this, the tissues were incubated for 12.5 min at 370C in PSS to which had been added (all from Sigma) bovine serum albumin (fatty acid free, 2.6 mg ml-'), papain (0.8 mg ml-'), collagenase (Type lA; 0.5 mg ml-1) and dithioerythritol ( The effects of various cations on the contraction produced by CPA were studied by construction of cumulative concentration-response curves for the cations against the increase in tone produced by 10 uM CPA (Gibson et al, 1994 The following drugs were used: A-9-C (anthracene-9-carboxylic acid; Sigma); cyclopiazonic acid (Sigma); BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N7,N7-tetraacetic acid; Sigma); caffeine (Sigma); DIDS (4,4' diisothiocyanato-stilbene-2,2'-disulphonic acid; Sigma); EGTA (ethylene glycol-bis(flaminoethyl ether) NNN',NY-tetraacetic acid; Sigma); nifedipine (Sigma); NG-nitro-L-arginine (Sigma); phentolamine mesylate (Ciba); guanethidine monosulphate (Sigma); SKF 96365…”

“…This is despite indirect evidence that store-regulated calcium entry occurs in these cells (van Breemen & Saida, 1989;Missiaen et al, 1990;Pacuad et al, 1993;Felder et al, 1994;Somlyo & Somlyo, 1994;Amrani et al, 1995). For example, in the mouse anococcygeus, the contraction to CPA, whilst being largely unaffected by nifedipine, is abolished in calcium-free extracellular medium and by the general calcium entry blocker, SKF 96365 (Gibson et al, 1994). …”

“…Recently we reported that cyclopiazonic acid (CPA), a mycotoxin isolated from Aspergillus and Penicillium, produces strong, well-sustained contractions of the mouse anococcygeus muscle (Gibson et al, 1994). CPA has been shown to inhibit sarco-endoplasmic reticulum (SR) calcium-ATPases and in doing so depletes these intracellular stores of calcium (Seidler et al, 1989;Imaizumi et al, 1992).…”