A quantitative relationship between cellular Na accumulation and relaxation produced by ouabain in the depolarized smooth muscle of guinea-pig taenia coli

Inhibition of calcium channels by harmaline and other harmala alkaloids in vascular and intestinal smooth muscles

“…Harmaline also inhibits Na', K+-ATPase in various tissues (Canessa et al, 1973;Becker & Willis, 1983). In smooth muscle, inhibition of Na', K+-ATPase leads to accumulation of cellular Na' and inhibition of contraction (Bose, 1975;Kishimoto et al, 1980). However, harmaline did not change the Na' content.…”

Species Differences in Inhibitory Effect of Li+ on High K+-lnduced Contraction in the Ileal Longitudinal Smooth Muscle

“…After a 60 min incubation with 68.4 mM Li+ (a half replacement for Na+) solution, monkey and rat ileum accumulated less Li+ than the guinea pig and rabbit ileum, whereas the contractions in monkey and rat ileum were more strongly inhibited than those in guinea pig and rabbit ileum. In guinea pig taenia coli, a correlation has been found be tween Li+-induced inhibition and Li+ content (5, 7) as well as in the case of Na+ (8,9,13). In the present study, a good correlation was found between the Li+ substitution-induced inhibition of 60K+-induced contraction and the intracellular Li+ content in the Heal muscles of all the animal species examined.…”

“…These results suggest that intracellular Li+ has a similar mechanism of inhibition as that of intracellular Nat It has been shown that the tonic com ponent of 60K+-induced contraction is due to the increase in Ca2+ influx across the mem brane in guinea pig taenia coli (14-16). It has also been shown that Li+-induced relaxation is antagonized by the increase in external Ca2+ and that intracellularly accumulated Li+ inhi bits 45Ca uptake, suggesting that both cellular Li+ and Na+ inhibits the high K+-induced in crease in Ca2+ influx in smooth muscle (5,7,8). However, when the intracellular free Ca2+ level and contractile tension were simul taneously recorded in guinea pig ileal strips loaded with a Ca2+ indicator, fura 2, Li+ substitution inhibited the 60K+-induced con traction but not the intracellular tree Ca2+ level (17).…”

“…Ouabain, a specific inhibitor of Na+,K+ ATPase, increases intracellular Na+ and inhi bits 60K+-induced sustained contraction in guinea pig taenia colt (8,9) and ileal longi tudinal smooth muscle from various animal species (9,10). In the ileal muscles, the ouabain-induced relaxation showed a species difference in two aspects: the inhibition by ouabain of Na+,K+-ATPase of the muscle and the sensitivity of muscle to accumulated Na+ (10).…”

Potassium-induced contraction in smooth muscle.

“…Accumulation of Na in the cell, induced by ouabain or vanadate, is reported to inhibit the voltage-dependent Ca channel (Kishimoto & Urakawa, 1982a;Kishimoto et al, 1980;Ueda et al, 1982).Intracellular Li may have a similar but more potent effect than intracellular Na (Kishimoto & Urakawa, 1982b). In contrast, bassianolide, a cyclodepsipeptide, inhibits the sustained contractions induced by various receptor-agonists (i.e., acetylcholine, histamine, serotonin and norepinephrine) whereas this inhibitor has no effect on the contraction induced by high K solution in guinea pig taenia coli, ileum and was deferens (Nakajo et al, 1982 …”