Influences of External Magnesium, Bicarbonate and Phosphate on Potassium-Induced Contracture of the Guinea Pig Taenia Coli

Abstract

It was reported that high-potassium (K) solution produced a contracture (K-induced contracture) in the guinea pig taenia coli, and the tension development in the muscle depolarized with high-K was dependent on calcium (1, 2), and that "Ca uptake and ex changeable fraction of cellular Ca increased with high-K (2).Furthermore, it was demonstrated that K-induced contracture was composed of phasic and tonic phases and was proposed that in the phasic contraction, sufficient calcium was released from a cellular site to initiate contraction, whereas in the tonic contraction, enough calcium crossed the membrane to initiate it and that the transmembrane calcium transport involved in the latter response was dependent on metabolism (3). On the basis of these results, the role of metabolism in the K-induced contracture of taenia coli was examined by the use of various metabolic intermediates, inhibitors of metabolism and active transport, revealing that the factors such as substrate removal, a decrease of tem perature, DNP, ouabain and a substitution of external sodium chloride with lithium chloride abolished the tonic response whereas the same factors had little or no effect on the phasic response.Hence it was considered that the phasic response was a passive process, while the tonic contraction was an active one depending on metabolism and possibly linked to active Na transport (4). This consideration was also supported by the electrophysiological experiments (5).In the present paper, further evidence was obtained concerning to the influences of the physiological components in the external media, that is, magnesium chloride (MgCl2), sodium bicarbonate (NaHCO3) and sodium phosphate (NaH2PO4) on the K-induced tension development of taenia coli. METHODSStrips of taenia coli (30-40 mg) were isolated from male guinea pigs weighing about 500 g. The excision of the muscle was endeavoured to avoid the Auerbach's plexus which includes the excitatory cholinergic nerve and intramural inhibitory nerve (6).

Effects of External Calcium and Some Metabolic Inhibitors on Barium-Induced Tension Changes in Guinea Pig Taenia Coli

“…Apparatus and procedure in these experiments were the same as those described in previous report (10).…”

Effects of Anion Substitutions on Potassium-Induced Phasic and Tonic Contraction in Taenia Coli

“…The apparatus, method of recording and the solutions used have been described in the previous article (7). After 30 minutes equilibration in the bath, the strips were challenged with high-K Tyrode solution at a final concentration of 42.7 mm KCl in all experiments, and 15 minutes application was performed.…”

“…After 30 minutes equilibration in the bath, the strips were challenged with high-K Tyrode solution at a final concentration of 42.7 mm KCl in all experiments, and 15 minutes application was performed. The time schedule of high-K application in the test was almost the same as that described in the previous paper (7).…”