Effects of temperature and inorganic ions on calcium accumulation in microsomes from intestinal smooth muscle

Response of the rabbit isolated testicular capsule at hypothermic and hyperthermic temperatures to norepinephrine, acetylcholine and prostaglandin F2 alpha

Spontaneous contractions of the adult rabbit isolated testicular capsule were found to be influenced by moderate hyperthermic and hypothermic temperature changes. The decrease in testicular capsular spontaneous contractions resulting from an exposure to 32, 40 and 42 degrees C have been shown to be influenced by the addition of NE, ACh and PGF2 alpha. Of the three neurohumoral agents studied, NE was found to cause the greatest increase and re-initiation of testicular capsular tone during both hypothermia and hyperthermia. These data indicate that endogenous levels of neurohumoral agents may play an important role in the maintenance of testicular capsular tone during exposure to hyperthermic or hypothermic conditions.

Cadmium reduces contractile responses of rat duodenum, in vitro

The present study focuses on the effects of cadmium in drinking water on rat duodenum contractility, in vitro. Two experimental groups (n = 10 each) were administered with 15 ppm cadmium chloride in their drinking water for 1 and 2 months, respectively. Two separate groups (n = 10 each) were maintained in similar conditions but received no cadmium and acted as controls. After the experimental period, the duodenal segment responses were measured by means of an isotonic transducer. The average peak amplitude of acetylcholine-induced contractions was significantly decreased in both cadmium-treated groups. Incubation of duodena from the cadmium-free controls with atropine or in a calcium-free medium resulted in reduced contractility that was undistinguishable from that of the cadmium-treated rats. Cadmium reduces the contractile response apparently by directly or indirectly decreasing cellular calcium influx.

Effect of treatment time on calcium antagonism by cadmium ions in a guinea-pig taenia coli

1. When pretreated for 1 min, with Cd2+ at low concentrations (0.001-0.01 mM), there was a parallel rightward shift of Ca2+ concentration-curves in guinea-pig taenia coli in K+-depolarized Ca2+-free medium. However, when pretreated for 30 min, Cd2+ reduced the maximal Ca2+ response size. 2. The application of 0.01 mM Cd2+ for 1, 5 and 30 min in Ca2+-free, K+-medium reduced to the same degree the Ca uptake after addition of 3 mM Ca2+. The inhibitory action on the tension by Cd2+ however, became greater as the pretreatment time with Cd2+ increased. 3. Within 5 min of Cd2+ (0.01 mM) treatment, Cd2+ chiefly bound to the cell membrane, however, with a longer duration (30 min), Cd2+ entered the cytoplasm where EDTA could not reach. 4. Cd2+ above 0.0005 mM reduced dose-dependently the respiration of isolated mitochondria. 5. These results suggest that with short duration exposure (1-5 min) of taenia coli cells to Cd2+, the interference with Ca2+ entry through voltage-dependent Ca2+ channels is predominant but for longer exposure times, intracellular actions of Cd2+ contribute to its inhibitory effects.

Potentiation of twitch contraction in guinea pig ureter by sodium vanadate

The effect of sodium vanadate on action potential and twitch contraction of guinea pig ureter was studied and compared with that of ouabain, elevated K+, low temperature, and a Ca agonist (BAY K 8644), which can be expected to exert certain comparative effects. Sodium vanadate markedly potentiated twitch contraction. Potentiation by vanadate was associated with marked prolongation of relaxation time. Sodium vanadate caused only slight depolarization of the membrane but marked changes in action potential. The duration of action potential was prolonged and the number of oscillatory spike potentials increased. These effects were different from those of other treatments. It is concluded that prolongation of action potential and the increase in the number of spikes are the main cause of potentiation of twitch contraction by sodium vanadate. In addition, inhibition of Ca pump activity of the smooth muscle membrane system by vanadate might also be involved in potentiation of twitch contraction.

The relaxation and Ca-pump inhibition in mesenteric artery of normotensive and stroke-prone spontaneously hypertensive rats

The influences of low temperature and vanadate, both of which have been known to inhibit the Ca-pump activity of membranous systems of smooth muscle cells, on the relaxation of mesenteric artery of stroke-prone spontaneously hypertensive rats (SHRSP) and normotensive Wistar-Kyoto rats (WKY) were studied. Relaxation was induced by the removal of extracellular Ca in high-K-depolarized preparations, so that the involvement of receptor kinetics and changes in membrane potential could be excluded. Relaxation was significantly slower in the preparation from SHRSP than in that from SHRSP. Low temperature prolonged relaxation in preparations from both SHRSP and WKY. No difference in the effect of low temperature was observed between the preparations, which showed Q10 values between 2.8 and 3.5 for 50 and 80% relaxation time. Sodium vanadate also prolonged the time course of relaxation in both preparations. No difference in the effect of sodium vanadate was observed between the preparations from WKY and SHRSP. These results suggest that Ca-pump activity is involved in the relaxation of K-depolarized smooth muscle of mesenteric arteries from both WKY and SHRSP. However, the difference in the pump activity may not contribute greatly to the difference in the relaxation of K-depolarized preparations by the removal of extracellular Ca.

Effects of cadmium ions, D-600 and KCN on calcium-45 uptake in smooth muscle of guinea-pig taenia coli

1. The effects of Cd2+ on Ca2+ uptake was compared with that of D-600 and KCN in guinea-pig taenia coli. Cd2+ inhibited both the phasic and tonic K+ responses, however, D-600 and KCN preferentially inhibited the tonic response. 2. Cd2+ (2 x 10(-6) M) which had no effect on the tissue ATP concentration, inhibited La3+ resistant residual Ca2+ binding at the high and low affinity site. Cd2+ (10(-5) M) which decreased the tissues ATP concentration, markedly inhibited Ca2+ binding at the low affinity site. 3. Both D-600 and KCN showed a greater inhibitory effect on Ca2+ binding at the low affinity site than at the high affinity site. 4. These findings suggest that Cd2+ at low concentration may inhibit Ca2+ influx through Ca2+ channel at surface membrane while at high concentrations (greater than 10(-5) M), Cd2+ would inhibit the accumulation of Ca2+ into low affinity sites relating to energy metabolism at mitochondria.

Effect of vanadate on cooling-induced tension changes in K-depolarized smooth muscles from guinea-pigs

Sodium vanadate reversed cooling-induced relaxation of K-depolarized taenia coli of guinea-pigs but failed to reverse it in the portal vein and uterus. It potentiated cooling-induced contraction of K-depolarized vas deferens and ureter. These effects were not mediated by the inhibition of Na,K-ATPase, but by the inhibition of the Ca-pump.

Effects of cadmium ions, D-600 and chlorpromazine on the skinned smooth muscle of guinea-pig taenia coli

The effects of Cd2+ on the skinned taenia coli were compared with that of Ca2+ channel blocker, D-600 and calmodulin inhibitor, chlorpromazine. The Cd2+ (0.001-0.5 mM) inhibited the contraction of skinned fibres in a dose-dependent manner. In contrast, the contraction of skinned fibres was not inhibited by pretreatment with 1 X 10(-6) M D-600. However, chlorpromazine (10(-4) M) inhibited the contraction of skinned taenia coli. The inhibition of contraction by Cd2+ in skinned taenia coli was completely reversed by washing with solution containing EDTA, following a treatment with 0.5 mM Cd2+ for 15 min. The skinned fibres had rapidly taken up a far greater amount of Cd2+ than intact muscle of taenia coli. EDTA increased Cd2+ efflux in skinned fibres and only 5% of the original tissue content retained. Thus, EDTA, which was ineffective on intact taenia coli, can be considered to act on Cd2+ of intracellular compartment after disruption of the cell membrane with saponin. In conclusion, there is the possibility that Cd2+ inhibits the contractile system, such as contractile proteins and calmodulin, which results in tension inhibitory effect.

The binding of cadmium ions to the smooth muscle of guinea-pig taenia coli

Taenia coli was used to study the property of binding of Cd2+. The Scatchard plots of cadmium uptake showed that two qualitative Cd2+ binding sites (high and low affinity binding sites) exist in taenia coli. Decrease in Ca2+ concentration in the medium did increase the cadmium binding. The Scatchard analysis of Cd2+ binding in taenia coli at 4 degrees indicated a single class of binding sites (only high affinity binding sites). These findings suggest that the greater number of high affinity Cd2+ binding sites in taenia coli may relate to the binding to cell membrane. Further, it was postulated that some of low affinity binding sites in taenia coli may reflect intracellular accumulation, indicating the action on the contractile system.

Temperature dependency of cadmium uptake and relaxant effect of cadmium in guinea-pig taenia coli

Cadmium fluxes were studied under low temperature in order to assess the site of action of Cd2+ in taenia coli. Following a treatment with 0.5 mM Cd2+ for 30 min at 37 degrees C, the responses to high-K+ were not reversed after washing with medium containing 0.5 mM disodium edetate (EDTA). However, at 30 min preincubation with 0.5 mM Cd2+ at 4 degrees C, the responses markedly returned by the washing. The cadmium uptake was much slower at 4 degrees C. The cadmium in muscle preincubated at 4 degrees C was markedly eliminated by EDTA. Thus, the increase in the size of the fraction of total cadmium not eliminated by EDTA was temperature dependent. These data suggest the possibility that the total cadmium not eliminated by EDTA in taenia coli may be accumulated in the intracellular compartment where EDTA cannot reach.

Time course of the spasmolytic effect of cadmium and cadmium uptake in guinea-pig taenia coli

The relationship between tension inhibitory action of cadmium and cadmium uptake was investigated in the smooth muscle of taenia coli. Following a treatment with 0.5 mM Cd2+ for short periods (1, 5 min), the tension to high-K+ returned to a greater extent after washing with disodium edetate (EDTA) or cysteine, compared to normal medium. However, the restored tension to the high-K+ decreased with increasing duration of Cd2+ treatment. With a longer duration of 0.5 mM Cd2+ treatment, the cadmium uptake increased and the size of cadmium fraction bound to cells firmly increased. It is suggested that Cd2+ binds initially to the surface membrane of taenia coli and that Cd2+ subsequently migrates to a compartment that EDTA cannot reach.

Modulation of cellular calcium stores in the perfused rat heart by isoproterenol and ryanodine

The inhibitory action of procaine on cellular calcium release was utilized to define a new cellular calcium pool which, under physiological conditions, is present only during catecholamine stimulation. Rat hearts labeled with 45Ca++ were perfused with medium containing procaine and EGTA at 23 degrees C to remove extracellular calcium, and then cellular calcium was released by removal of procaine and restoration of calcium. By this method we have identified a cellular calcium pool (pool C) whose release is inhibited by procaine, but which does not require extracellular calcium for its release. Release of pool C can also be triggered by caffeine. [We have previously identified a cellular calcium pool (pool A) whose release is triggered by caffeine, inhibited by procaine, and which does require extracellular calcium for its release.] When hearts were labeled for 3 minutes with perfusate containing 1 mM 45Ca++, 48 +/- 6 nmol Ca++/g wet weight was found in pool A, but only 3 +/- 1 nmol Ca++/g in pool C. However, if isoproterenol was present during labeling, the hearts contained 72 +/- 5 nmol Ca++/g in pool A and 42 +/- 6 nmol Ca++/g in pool C. When calcium concentration in the labeling perfusate was varied, with and without isoproterenol, it was found that pool C does not begin to fill until pool A is almost full. The same effect was seen when excess cellular calcium uptake was induced by removing sodium from the perfusate. Ryanodine (0.2 microM) induced contractile failure (t1/2 = 3.4 +/- 0.4 min) and depleted pool A in control hearts by 85%. Ryanodine also similarly depleted pools A and C in isoproterenol-treated hearts. When contractility was monitored at the same time as the hearts were labeled, a linear relationship between dP/dt and the sum of pools A and C was observed over a wide range of conditions. Pools A and C both selected strongly for calcium over barium. These observations suggest that both pools A and C are located in the sarcoplasmic reticulum and are intimately involved in the regulation of contractility.

Some properties of Ca-binding microsomal subfractions isolated from rabbit colon muscle

From a homogenate of rabbit colon smooth muscle a microsomal fraction was isolated, which was divided into subfractions by centrifugation on a discontinuous sucrose gradient. The Ca-binding properties of the subfractions were investigated under different conditions. In the presence of 0.35 mM ATP the Ca binding of the fractions amounted to 4--8 nmol/mg protein. The 35% fraction bound more Ca per mg protein than the 35--45% fraction. The Ca accumulation was comparatively higher both in the presence of 5 mM ATP and in the presence of 5 mM oxalate. The two fractions showed about the same sensitivity for oxalate. This substance stimulated the Ca uptake at 5 mM but not at lower concentrations. The amount and the rate of Ca binding were more dependent on variations in the exogenous ATP concentration in the 35% fraction than was the case for the 35--45% fraction. The Ca binding was completely inhibited by salyrgan when the microsomal fractions were pretreated with this agent. Sodium azide did not influence the Ca-binding capacity of the fractions. It is suggested that the microsomal subfractions of the rabbit colon muscle represent physiologically important parts of the Ca sequestering system of the muscle, since Ca binding takes place at Ca- and ATP-concentrations which are believed to be present in the myoplasm.