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This work deals with study, of effect of yttrium acetate (Y3+) on myocardium of the frog Rana redibunda and of its action on the ion transport across the inner membrane of the rat heart mitochondria. It was found that Y3+ decreased strength of heart contractions and facilitated transport of ions in rat heart mitochondria stimulated by 10 mM glutamate and 2 mM malate. In the presence of Y3+, the energy-dependent transport of Ca2+ in mitochondria was inhibited; this was manifested as a decrease of their swelling in the medium containing 125 mM NH4NO3 and Ca2+ or 25 mM potassium acetate, 100 mM sucrose and Ca2+. It is assumed that the Y(3+)-caused decrease of the heart muscle contractility is not only due to its direct blocking effect on the potential-operated Ca2+ channels of the pacemaker and contractile cardiomyocytes, but also due to its mediated action on active transport of Ca2+ in mitochondria. The data that Y3+ activates transport of K+ via the mitochondrial potassium uniporter and blocks Ca(2+)-channels of the inner mitochondrial membrane are important for better understanding of mechanisms of action Y3+ on cardiomyocytes of vertebrate animals and humans and the possible use of Y3+ in medicine.

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Vascular smooth muscle of the frog was skinned by 0.2 mg/ml saponin for 20 mm. The skinned preparations activated by Ca2+, at 2 mmol/l Mg2+ and MgATP2-, gave half maximal force at Ca2+ = (1.32 +/- 0.07) x 10(-6) mol/l and maximal force at Ca2+ = 3.16 x 10(-5) mol/l (35 +/- 4% of the maximal contraction induced by KCl in living smooth muscles). The Hill coefficient was 1.51 +/- 0.11. Thus, the skinned vascular smooth muscle of the frog has Ca2+ sensitivity similar to that of various preparations from a variety of muscle types; the slope of the tension-pCa curve obtained was similar to that typical of mammalian smooth muscles.

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The mechanism of action of MD1, a new biotechnological radiotherapeutic agent of plant origin, on smooth muscle contraction was investigated. Contraction induced by MD1 consists of an initial dose-dependent transient phasic response (PR) (with ED50 = 0.11 +/- 0.02%, n = 4, the time of rise 15 s, onset of decay about 30 s) followed by a tonic contraction (TC) (at 10% MD1 only) with a maximum in 20 min (0.78 +/- 0.07 x the maximum contraction induced by 110 mmol/l KCl, n = 8, (TC/PR) = 0.94 +/- 0.11, n = 5). If the vessel was washed out during this maximum, the maximum tension was maintained for up to 2 h ("long-lasting" tension) and was abolished after perfusion with Ca(2+)-free EGTA solution (E) or H7 (0.05 mmol/l) solution. With solution E being applied 30 min before 10% MD1-induced contraction, TC was reduced by 92 +/- 3% (n = 4) in contrast to PR being reduced by 48 +/- 5% (n = 5). During TC, calcium appeared to penetrate into cells through receptor operated channels, since tension neither depended on verapamil (0.05 mmol/l) nor cobalt (up to 10 mmol/l). In solution H7 (with 10 min pretreatment), PR and TC were almost completely inhibited. It is proposed that MD1 activates the C-kinase branch of the calcium messenger system.

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The thermal dependence of the force-velocity relation (P - V) in thin (20-40 fibres) live twitch muscle bundles from suction apparatus of lamprey by force-clamp method was investigated. The P - V relation was hyperbolic and Hill's constants were as follows: a/P0 was 0.13 +/- 0.01 and 0.08 +/- 0.01 (mean +/- S.E.M.), b was 0.46 +/- 0.02 and 0.65 +/- 0.03 at 8 degrees C and 18 degrees C, respectively. The maximal isometric tension (P0) was about 100 mN/mm2 at 8 degrees C, 18 degrees C, and 22 degrees C. After the temperature was switched from 8 degrees C to 18 degrees C, the dependence of P0 on incubation time was observed. The maximal power output determined from P - V relation using Hill's equation was 0.062 +/- 0.002 and 0.056 +/- 0.001 at 8 degrees C and 18 degrees C, respectively. The maximal velocities of shortening (V0) were 3.9 +/- 0.1 L0/s and 7.2 +/- 0.2 L0/s at 8 degrees C and 18 degrees C, respectively. Q10 for V0 in this range of temperatures was 1.86. a/P0 and power output were about 2 times lower than those reported in literature for other animals. In general, the thermal dependence of the parameters studied was similar to those reported for fish muscles and skinned lamprey muscles, P0 being relatively independent, V0 highly dependent, and a/P0 inversely dependent on temperature.

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