Effects of rapid cooling on the mechanical and electrical activities of smooth muscles of guinea pig stomach and taenia coli

Saline volume required to achieve peristaltic intraluminal pressure during leak testing of canine colotomies, using two methods of luminal occlusion

Background

No studies have appeared in the literature evaluating the intraluminal volume of injected saline in the canine colon for performing leak tests in colotomy incisions.

Aim

To determine the volume of the injected intraluminal saline necessary to achieve an intraluminal pressure of 17.3 cm H2O in 10 cm colonic segments containing a closed colotomy occluded with intestinal forceps or by digital pressure.

Methods

Fresh colon was obtained from 8 canine cadavers and divided into 10 cm segments. A 3 cm antimesenteric colonic incision was performed at each intestinal segment which was closed using a 3-0 polydioxanone suture in a simple continuous pattern. Each colonic construct was occluded with Doyen intestinal forceps or by digital pressure and a leak test was performed by saline infusion. The saline volume needed to achieve a predetermined intraluminal pressure of 17.3 cm H2O, following occlusion was recorded.

Results

The mean volume of injected saline with the Doyen intestinal forceps occlusion (20.4 ± 8.2 ml) was significantly larger than that of the digital occlusion technique (17.5 ± 6.8 ml) [p = 0.021].

Conclusion

For 10 cm canine colonic constructs containing a closed colotomy, saline volumes of 20.4 ml with Doyen occlusion and 17.5 ml with digital occlusion can be utilized to achieve intraluminal pressures of 17.3 cm H2O.

Continuous cooling system in conjunction with laser surgery for ear reshaping

When the cartilage on the prominent ears is reshaped, the arising stress returns the tissue to its initial configuration. Laser irradiation of areas of maximal stress leads to stress relaxation and results in a stable configuration. Sixty auricles were harvested from 30 New Zealand white rabbits and cut into a rectangle measuring 50 mm by 25 mm with an average thickness of approximately 1.3 mm. Bilateral skin was included for ex vivo studies. Continuous cryogen spray cooling (CSC) with laser energy was delivered to the exposed cartilage for reshaping. In clinical applications, from January 2006 to December 2016, a total of 50 patients with 100 bat ears who underwent CO₂ laser reshaping (otoplasty) were assessed. A continuous cooling system (4 °C) in conjunction with a CO₂ laser was applied to make a retroauricular-approached incision and reshape the ear cartilage. The well cartilage bending correlated with the different parameters demonstrated in the continuous CSC protected group. All 100 (100%) of the subjects experienced early complications (≤ 1 month) related to laser exposure with swelling, while 5 (5%) experienced ecchymosis, 2 (2%) minimal hematoma, 2 (2%) scarring, 1 (1%) minor infection, 1 (1%) under correction, 1 (1%) overcorrection, and 1 (1%) relapse. These problems were corrected and/or had resolved after 3 months. All patients achieved good to excellent results in our final outcome assessment (> 6 months). Laser reshaping has a potential use in certain surgical procedures involving the cartilage. The appropriate conditions for laser ear reshaping clearly depend on the laser wavelength used, energy controlling, and tissue optical properties.

The time-dependent and dose-dependent effects of caffeine on the contraction of the ferret heart

1. Trabeculae isolated from ferret heart and from other mammalian hearts have been mounted in a way that enables the tension generated to be measured while the composition of the bathing fluid is rapidly altered.2. Application of caffeine to these trabeculae initiates a rapid transient contracture and depresses the strength of regularly evoked heart beats.3. The strength of the contractures, the rate of tension development and the rate of spontaneous relaxation are all increased by raising the concentration of the applied caffeine.4. The strength of the caffeine contracture is relatively unaffected by changes in the bathing Na(+), K(+) or Ca(2+) concentrations, but is reduced by exposure to the free-base form of local anaesthetics.5. Lowering of the temperature has complex effects on the amplitude of the caffeine contracture due to the differing temperature sensitivities of the contraction and spontaneous relaxation.6. Following a caffeine contracture, a period of perfusion by caffeinefree solution is required before a full-sized contracture can be evoked by the re-application of caffeine. This re-priming of the caffeine contracture has a sigmoidal time course that can be fitted by a two compartment model. The rate constants of the filling of each of the compartments can be obtained analytically, and are found to be increased by raising the extracellular calcium concentration, [Ca](o), by stimulating the preparation or by raising the temperature. Reducing the [Na](o) or raising the [K](o) has little effect on these processes.7. The presence of traces of caffeine in the perfusing fluid between the conditioning and test challenges with the caffeine contracture solution reduces the extent of the re-priming without much affecting its rate.8. The behaviour of several model systems have been compared with that of the heart with the aid of an analogue computer. A four compartment closed system has been found to simulate the results presented in this paper.9. It appears that caffeine has its effects by acting to increase the rate of release of activator calcium from one part of a non-homogeneous intracellular relaxing system present within the mammalian heart, which is likely to be the sarcoplasmic reticulum.

New thermal wave aspects on burn evaluation of skin subjected to instantaneous heating

Comparative studies on the well-known Pennes' equation and the newly developed thermal wave model of bioheat transfer (TWMBT) were performed to investigate the wave like behaviors of bioheat transfer occurred in thermal injury of biological bodies. The one-dimensional TWMBT in a finite medium was solved using separation of variables and the analytical solution showed distinctive wave behaviors of bioheat transfer in skin subjected to instantaneous heating. The finite difference method was used to simulate and study practical problems involved in burn injuries in which skin was stratified as three layers with various thermal physical properties. Deviations between the TWMBT and the traditional Pennes' equation imply that, for high flux heating with extremely short duration (i.e., flash fire), the TWMBT which accounts for finite thermal wave propagation may provide realistic predictions on burn evaluation. A general heat flux criterion has been established to determine when the thermal wave propagation dominates the principal heat transfer process and the TWMBT can be used for tissue temperature prediction and burn evaluation. A preliminary interpretation on the mechanisms of the wave like behaviors of heat transfer in living tissues was conducted. The application of thermal wave theory can also be possibly extended to other medical problems which involve instantaneous heating or cooling.

Mechanism of carbachol-evoked contractions of guinea-pig ileal smooth muscle close to freezing point

1. The effect of lowering the temperature to near freezing-point upon the contractions and [3H]-inositol phosphate responses to carbachol were investigated in longitudinal smooth muscle from the guinea-pig ileum. 2. The peak amplitude of the contraction to a single application of 100 microM carbachol was the same at 37 degrees C and temperatures near freezing-point. However, the sensitivity to carbachol was reduced upon lowering the temperature and the time to peak contraction was increased from 5-10 s to 2-10 min. Even when the temperature was maintained near freezing-point, washing off carbachol produced a relaxation and eventual return of tension to basal levels. 3. Incubating the tissue in 140 mM K+, calcium-free solution or in calcium channel antagonists significantly reduced the carbachol-induced contraction to 10-30% of the control at 37 degrees C and also at 3 degrees C. Thus the majority of the activator calcium required for contraction entered the tissue via voltage-dependent calcium channels (VDCs) at both 37 degrees C and 3 degrees C. 4. The contractions produced by high potassium solutions were less at temperatures close to freezing-point than those at 37 degrees C suggesting that voltage-dependent calcium entry was inhibited as the temperature was lowered. 5. A small part of the contractile response to 100 microM carbachol was resistant to the removal of extracellular calcium at both 37 degrees C and 3 degrees C and this component was increased under depolarizing conditions. This suggests that the release of stored calcium contributes to a minor degree to contraction at both 37 degrees C and 3 degrees C.6. Although 100 microM carbachol produced a statistically significant rise in several [3H]-inositol phosphate isomers at both 37 degrees C and 3 degrees C, the production of [3H]-inositol phosphates was less at 3 degrees C than at 37 degrees C and the increase in their production caused by carbachol was much slower.7. These results suggest that the carbachol-induced contraction at 3 degrees C utilizes both calcium entry through VDCs and calcium release from intracellular stores, as at 37 degrees C. The components of the responses dependent upon intracellular calcium release at 37 degrees C and at temperatures near freezing-point were similar. However, the production of [3H]-inositol phosphates, including the calcium-mobilizing second messenger inositol (1,4,5) trisphosphate (Ins(1,4,5)P3), is reduced at such low temperatures.

A slow calcium-dependent chloride current in rhythmic hyperpolarization in neurones of the rabbit vesical pelvic ganglia

1. Voltage-clamp recordings were made from neurones of vesical pelvic ganglia isolated from the rabbit urinary bladder. A rhythmic outward current, ISH, which corresponds to the spontaneous hyperpolarization, occurred at fairly constant intervals in fifty-eight of eighty-four neurones superfused with Krebs solution. The peak amplitude of the ISH was 0.5 +/- 0.2 nA (n = 48; mean +/- S.E.M.). 2. The ISH was eliminated in a Krebs solution containing nominally zero calcium and 12 mM-magnesium. Lowering the temperature of the superfusing solution from 36 to 22 degrees C also inhibited the occurrence of the ISH. 3. Bath application of caffeine increased the frequency of ISH. In contrast, ryanodine and procaine reversibly blocked ISH. 4. In thirty-four of fifty-eight neurones, the ISH was composed of two current components, an initial fast ISH with duration of 1-10 s and a slow ISH lasting 15-60 s. In the remaining twenty-four neurones, ISH showed only the fast component. 5. The fast ISH was associated with an increased membrane conductance and the slow ISH was associated with a decreased membrane conductance. The reversal potentials of the fast and the slow ISH were -88 +/- 7 mV (n = 4) and -30 +/- 6 mV (n = 4), respectively. 6. Tetraethylammonium (5 mM) and barium (1 mM) blocked the fast ISH but not the slow ISH. Intracellular caesium injected by ionophoresis through a Cs(+)-filled microelectrode blocked the fast ISH, without affecting the slow ISH. Apamin and (+)-tubocurarine selectively suppressed the fast component of the ISH. 7. Substitution of isethionate (67 mM) for chloride increased the amplitude of the slow ISH and shifted the reversal potential of the slow ISH to +1 +/- 8 mV (n = 5). A slow ISH with amplitude of 0.1-1 nA and was still observed in a low-sodium (26.2 mM) solution. The stilbene derivative, 4-acetamido-4'-isothiocyanostilbene-2,2'-disulphonic acid (SITS), a chloride channel blocker, suppressed the slow ISH. 8. These results suggest that ISH is composed of two distinct calcium-dependent currents, a fast ISH produced by activation of potassium conductance and a slow ISH produced by inactivation of chloride conductance. 9. The after-hyperpolarization (AHP) following the action potential was also composed of apamin-sensitive and insensitive spontaneous hyperpolarizing oscillations. The apamin-insensitive component of IAHP was increased by lowering external chloride activity, while it was depressed by SITS.

Evidence for extracellular localization of activator calcium in dog coronary artery smooth muscle as studied by the pyroantimonate method

Correlated physiological and electron-microscopic studies were made on the source of calcium activating the contractile system (activator calcium) in dog coronary artery smooth muscle fibers. The magnitude of contracture tension induced by 100 mM K+ was dependent on external Ca2+ concentration and reduced or eliminated by factors known to reduce the Ca2+ spike or Ca2+ influx. Little or no mechanical response was elicited by treatments known to cause release of intracellularly stored calcium. These results indicated that the contractile system is mainly activated by the inward movement of extracellular calcium. In accordance with the physiological experiments, electronopaque pyroantimonate precipitate containing calcium was found in the lumina of caveolae, but not in any intracellular structures close to the plasma membrane, when the relaxed fibers were fixed in a 1% osmium tetroxide solution containing 2% potassium pyroantimonate. If the contracted fibers were fixed in the same solution, the pyroantimonate precipitate was diffusely distributed in the myoplasm in the form of numerous particles, while the precipitate in the caveolar lumina was scarcely seen. These findings are discussed in connection with the regulation of intracellular Ca2+ concentration in dog coronary artery smooth muscle.

Facilitating effect of cold shock on recovery from anoxia-induced contractile depression in isolated rat heart and heart muscle

The effect of rapid cooling on the recovery process from anoxia-induced hypodynamic state was studied in isolated rat ventricular muscle and ventricle. Following 10-15 minutes' perfusion of N2-saturated Krebs solution, the muscle was reoxygenated. When the muscle was rapidly cooled for 10-30 seconds during the early phase of reoxygenation, the rate of recovery from contracture significantly increased (p less than 0.01). Rapid cooling was also effective on the recovery from contracture induced by superfusion of Krebs solution with lowered sodium chloride concentration, but it did not affect the recovery from rigor induced by CN-. In the recovery from sustained anoxia (60 minutes), cooling facilitated reattainment of tension development and reduction in contracture tension. Similarly, in whole heart, 2-3 episodes of rapid cooling for about 60 seconds significantly accelerated the recovery of pressure development after 30 minutes of anoxia. At 60 minutes after reoxygenation, pressure development in hearts that were reoxygenated without rapid cooling was 29.8 +/- 26.9% (mean +/- SD) of pressure developed before anoxia. This value increased to 93.8 +/- 27.5% following recurrent rapid cooling (p less than 0.001). At the same time, rapid cooling prevented any significant elevation in resting tension (development of oxygen paradox). These results indicate that excess intracellular calcium ions were removed by rapid cooling. This relief of the myocardium from calcium overload is believed to improve mitochondrial function and result in facilitated recovery of contractile activity.

Carbachol contracture of stomach smooth muscle of the newt in calcium-free solution

A small muscle preparation of stomach circular muscle of the newt responded to carbachol (CCh) with a phasic contracture. At 20 degrees C, in Ca-free Ringer solution (+1 mM EGTA), the amplitude of CCh contracture was very rapidly inhibited to less than 10% of that in normal Ringer solution (1.8 mM Ca). The amplitude of this CCh contracture was markedly enhanced with increasing [K]0. CCh contracture in Ca-free Ringer solution was also enhanced after K contracture was induced once in the presence of 1.8 mM Ca, followed by soaking in normal Ringer solution. The amplitude of this enhanced CCh contracture persisted up to about 5 min, following rapid decrease to about 70%, and then gradually decreased to a steady level in Ca-free Ringer solution. This decrease in amplitude was prevented by increasing [K]0 during soaking in Ca-free solution; even when the temperature was elevated from 20 to 35 degrees C during the periods of soaking in Ca-free solution, CCh contracture was inhibited only by about 20% in Ca-free high K solution, whereas in Ca-free or Ca-free low Na (Tris) Ringer solution it was inhibited by more than 50%.

Some properties and mechanisms of thymol-induced release of calcium from the calcium-store in guinea-pig taenia caecum

The properties and mechanisms of Ca release induced by thymol from the intracellular Ca-store in the guinea-pig taenia caecum were investigated and compared with those by carbachol, using an intact muscle and a microsomal fraction. In Ca, Na-free, EGTA-containing K-solution, a transient contraction was evoked by each drug, and carbachol produced the contraction following treatment with thymol; however, a reversed sequence did not. The efflux of preloaded 45Ca in the presence and absence of ATP from taenia microsomes was accelerated by increasing concentrations of Ca ions outside. The minimal concentration to stimulate 45Ca-efflux was below 0.2 microM in both cases, and the Km values for Ca ions in the presence and absence of ATP were estimated to be 0.65 microM and 2.0 microM Ca ions, respectively. Thymol, which has been reported to be one of the most potent stimulators of the Ca-induced Ca release in the sarcoplasmic reticulum of skeletal muscle, enhanced the 45Ca-efflux from the taenia microsomes in the presence of ATP dose-dependently, and its mode of action seemed bimodal. That is, at 0.5 mM, thymol lowered the concentration of Ca ions which are needed to induce stimulation of 45Ca-efflux, whereas, at 1 mM, the stimulative effect of thymol on 45Ca-efflux was to augment the maximum rate of 45Ca-efflux, independent of concentrations of Ca ions. Carbachol (1 mM) did not have an effect on 45Ca-efflux with or without 0.1 mM GTP. In conclusion, the possibility has been suggested that in the guinea-pig taenia caecum, carbachol might release stored Ca ions via unknown pathway(s), whereas thymol directly releases Ca ions in a ATP-regulated fashion. Further, carbachol would be more efficacious for releasing stored Ca ions. Notwithstanding, the Ca-stores and/or the Ca-releasing mechanisms, which are utilized by both thymol and carbachol, seemed to share a common part(s) to some degree.

The effects of K+-depolarization medium, chelating agents and thiol groups on cadmium uptake and efflux in the guinea-pig taenia coli

Cadmium uptake by taenia coli was dose-dependent, achieving equilibrium after approximately 60 min of incubation. The SH-blocker, N-ethylmaleimide inhibited cadmium uptake. When muscles were washed with normal medium or that containing 0.5 mM EDTA following 0.5 mM Cd2+ treatment for 60 min, the tissue cadmium concentration reached equilibrium levels after 60 min and approximately 43 or 27% of the initial tissue cadmium concentration was retained, respectively. Both glutathione and dithiothreitol also increased cadmium efflux. However the contractions of glycerinated taenia coli caused by Ca2+ and Mg-ATP, completely returned to control values after washing with 0.5 mM EDTA medium following 0.5 mM Cd2+ treatment for 60 min, suggesting that EDTA seems to exert intracellular effects in glycerinated taenia coli. These results suggest that SH-dependent mechanisms in cadmium uptake play a role in intact taenia coli. In addition, in intact taenia coli, Cd2+ are accumulated in intracellular compartments which EDTA cannot reach and may exert an inhibitory action on internal sites in the cells.

Calcium-dependent after-potentials in visceral afferent neurones of the rabbit

Intracellular recordings were made from neurones in nodose ganglia excised from rabbits. In C neurones, 1-60 action potentials were followed by an after-hyperpolarization with a peak amplitude of 16 mV and a time constant of decay ranging from 3 to 10 s. In A neurones, the action potentials were followed only by a brief (up to 50 ms) after-hyperpolarization. The after-hyperpolarization was associated with an increase in the membrane conductance to potassium ions; it reversed polarity at the potassium equilibrium potential. The increase in conductance following the action potentials was blocked by removal of calcium ions, or addition of cobalt to the extracellular solution. Intracellular injection of ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid (EGTA) abolished the after-hyperpolarization; intracellular injection of calcium mimicked the after-hyperpolarization. It is concluded that calcium entry during the action potential leads to a long-lasting increase in potassium conductance in visceral afferent C neurones.

Cooling-induced contraction in ileal longitudinal smooth muscle of guinea-pig

The ileal longitudinal smooth muscle developed a transient contraction on cooling from 37 degrees C to 1 degree C in normal Ca2+ (2.5 mM) medium. The transient contraction was not inhibited by pretreatment with the Ca2+ antagonist, D-600 (1 X 10(-6)M). The contractions were sustained by cooling to 1 degree C in the presence of added Ca2+ greater than 10 mM. After the pretreatment with D-600, when the muscle incubated in normal medium with added 20 mM Ca2+ had been cooled to 1 degree C, a phasic response was only seen. However, D-600 did not inhibit the sustained contraction at 1 degree C after incubation in the presence of added 20 mM Ca2+. It is suggested that the transient and sustained contraction at 1 degree C is maintained by Ca2+ release from a cellular site, probably the cell membrane and it requires more calcium for the sustained tension.

Release of calcium ions linked to the activation of potassium conductance in a caffeine-treated sympathetic neurone

1. The mechanism of spontaneous and rhythmic hyperpolarizations which occur in bullfrog sympathetic ganglion cells under the effect of caffeine (2--10 mM) were further analysed. 2. Intracellular injection of EGTA blocked generation of caffeine hyperpolarizations (C-hyperpolarizations): this confirmed the previous conclusion (Kuba & Nishi, 1976) that these hyperpolarizations are caused by rhythmic increases in the K+ conductance (GK) of the membrane as a result of rises in free intracellular Ca2+. 3. The amplitude and duration of a C-hyperpolarization induced by an action potential was a function of the time since the previous one; the longer the interval, greater the area. 4. The relationship between the product of the amplitude and duration of a C-hyperpolarization and the preceding interval depended on external Ca2+; when this was low the relationship shifted, so as to indicate an involvement of a Ca2+ accumulating process in the generation mechanism of C-hyperpolarizations. 5. A rapid lowering of temperature triggered the generation of a C-hyperpolarization before appearance of a rhythmic one. There seemed to be no threshold temperature for the effect of such a cold shock; cooling from any temperature within a certain range (10--25 degrees C) by more than a few degrees was effective. 6. The rapid cooling effect was observed even in a Ca2+-free Mg2+ solution. 7. Dantrolene Na increased the interval between rhythmic C-hyperpolarizations or blocked them, but affected less those triggered by an action potential or cold shock. 8. Intracellular injection of Ca2+ triggered the generation of a C-hyperpolarization before the appearance of a rhythmic one. 9. The latency of the generation of an action potential-evoked C-hyperpolarization was dependent on the preceding interval; the shorter the interval, the longer the latency. There was a refractory period for induction of an action potential-induced C-hyperpolarization. 10. The interval between rhythmic C-hyperpolarizations was increased by a small or moderate membrane hyperpolarization (5--20 mV) and decreased by a larger hyperpolarization; the refractory period of an action potential-induced C-hyperpolarization was similarly increased and then decreased by progressive membrane hyperpolarization. 11. These results suggest that rhythmic increases in the GK under the effect of caffeine are due to oscillations of the intracellular Ca2+ concentration and that there may be Ca storage sites in the bullfrog sympathetic ganglion cell which are comparable to the sarcoplasmic reticulum in the skeletal muscle fibre.

Effects of diltiazem on electrical and mechanical activities of isolated guinea pig taenia coli

Effects of diltiazem on electrical and mechanical activities of isolated guinea pig taenia coli were studied by means of the double sucrose-gap method. In the spontaneously active preparations, diltiazem (2.2 X 10(-6) M) suppressed both electrical activity and isometric contraction, while electrical and mechanical activities evoked by the depolarizing current pulse were not affected at the concentration of 2.2 X 10(-6) M. In the presence of 2.2 X 10(-5) M diltiazem, the evoked contractile force and the number of repetitive firings during depolarization were reduced, whereas the single spike was almost unchanged or somewhat inhibited. At 2.2 X 10(-4) M diltiazem, both electrical and mechanical activities were almost abolished. The contractile force and single spike suppressed by diltiazem were partly reversed by the addition of 5 mM CaCl2. There was little significant change in membrane potential and membrane resistance. Similar but somewhat weaker effects were observed when NaCl was replaced with sucrose. In some preparations, 2.2 X 10(-4) M diltiazem reduced the contractile force without significant influence on the electrical activity in Na+-free Locke solution. CoCl2 (3 mM) inhibited the evoked activities in both normal and Na+-free solutions. Possible mechanisms for the relaxing effects of diltiazem on isolated guinea pig taenia coli were discussed.

Some differences in contractile responses of isolated longitudinal and circular muscle from the guinea-pig stomach

The mechanical and electrical properties of the longitudinal (fundus and corpus) and circular (antrum) muscle fibres of the guinea-pig stomach were investigated. 1. In the longitudinal but not in the circular muscle isotonic K Krebs and Na-free (sucrose) Krebs solutions produced a contracture with a tonic component. The different mechanical responses were not accompanied by different membrane responses. Verapamil abolished both phasic and tonic components of K-induced contracture. 2. During the tonic response of the K-induced contracture, repolarization of the membrane by current pulses relaxed the tissue; after cessation of the current pulse, rebound contracture occurred. In the circular muscle, the Q10 value for the rate of relaxation induced by inward current pulse was 3-1 and for the development of rebound contracture was 2-4. 3. After the tissue had been immersed in Ca-free isotonic K Krebs solution, application of Ca produced a large contracture in the longitudinal muscle, but contracture in the circular muscle was small or absent. However, the amplitude of subsequent carbachol-induced contracture in the above solution was enlarged in proportion to the durations of Ca treatment in both tissues. 4. Direct tetanic electrical stimulation could produce tension in both tissues. With low frequency of stimulation (0-1 Hz) a positive staircase was observed in the circular but not in the longitudinal muscle. 5. It is concluded from these results that topical differences of the motility in the stomach may be due not only to the activity of nervous elements, but also to differences in the properties of the muscle fibres themselves.

The effects of caffeine on the contraction of the frog heart

1. The force of contraction and the membrane potentials have been measured from preparations of frog heart, with methods that also allow the rapid exchange of the extracellular fluid.2. In regularly beating preparations, caffeine induces only weak contractures at temperatures above 15 degrees C, but it does cause a marked potentiation of the twitch responses; longer exposure results in a depression of contraction. The build up and decline of the twitch strength, on addition and on removal of caffeine approximates to a single exponential, time constant 26-45 sec, and this time constant is not altered by variation of the [Ca](o), the stimulus rate or the caffeine concentration. This time course of the change of twitch strength is less complex than the changes seen when either [Ca](o) or the stimulus rate is altered, suggesting a more direct action of caffeine on excitation-contraction coupling.3. Caffeine increases the strength of the contractures initiated by potassium-rich or sodium-depleted solutions in isolated atrial trabeculae.4. After the spontaneous relaxation of the contracture, evoked by either sodium-free or potassium-rich fluids, the application of caffeine initiates a redevelopment of tension. This caffeine contracture is transient and its strength is dependent on the caffeine concentration. The response in sodium-free solution can be elicited in the virtual absence of extracellular calcium.5. Local anaesthetics antagonize the caffeine contracture.6. The results suggest that the sarcoplasmic reticulum of frog heart muscle plays an important role in the initiation and control of contraction and relaxation.

Effects of rapid cooling on the electrical properties of the smooth muscle of the guinea-pig urinary bladder

The effects of low temperature (36-10 degrees C) on the electrical properties of smooth muscle cells of the urinary bladder were investigated with microelectrodes and the double sucrose gap method.1. Lowering the temperature from 36 to 20 and to 10 degrees C, depolarized the membrane from -37 to -33 and to -25 mV respectively. Spontaneous and propagated spike activity ceased completely at below 20 degrees C but evoked spikes were occasionally observed at 10 degrees C. A sustained contracture was evoked below 25 degrees C.2. At both normal and low temperatures, the tissue had cable-like properties. The length constant was reduced from 1.82 mm (36 degrees C) to 1.54 mm (20 degrees C) and to 1.04 mm (10 degrees C). On the other hand, the time constant of the membrane calculated from the cable equations was prolonged by lowering the temperature from 157 msec (36 degrees C) to 257 msec (20 degrees C) and to 508 msec (10 degrees C). The effective resistance of the membrane was increased to 1.8 times at 20 degrees C and to 2.9 times the control value at 10 degrees C.3. From the changes in various parameters of the membrane at low temperature, an increase in the longitudinal resistance of the tissue was postulated.4. The possible mechanisms of action of low temperature on the electrical properties of the smooth muscle of the urinary bladder were discussed in relation to those of the taenia coli and stomach, especially on the effects of low temperature on the sequestered Ca in the cell.

Effects of thymol on the electrical and mechanical properties of the guinea-pig taenia coli

Effects of thymol (0.02-2 mM) on the electrical and mechanical activities of the smooth muscle cells of the guinea-pig taenia coli were investigated with either micro-electrode or double sucrose gap methods.1. Thymol, in a concentration of more than 0.03 mM, reduced the amplitude and maximum rate of rise of the spikes without any change of the membrane potential. When the concentration was increased to 0.3 mM, thymol completely blocked the spontaneous and evoked spike activities. In a concentration of more than 0.1 mM, thymol reduced the membrane resistance in proportion to the concentration without any change of the membrane potential.2. Ionic mechanisms involved in the effects of thymol on the membrane resistance were investigated in various ionic environments. The results showed that in concentrations below 0.5 mM thymol might selectively increase the Cl-conductance of the membrane. Participations of Na and K ion in the effects of thymol on the membrane resistance could be eliminated. However, at more than 1 mM, thymol increased the membrane conductance non-selectively. Excess Ca in the external solution partly suppressed the action of thymol on the taenia coli.3. Potentiation of the twitch tension was not observed on treatment with any concentration of thymol.4. After pre-treatment with thymol (0.5 mM), isotonic K Krebs solution depolarized the membrane and reduced the membrane resistance as observed in the absence of thymol. However, thymol completely suppressed the K-induced contracture.5. Application of excess Ca and acetylcholine during the maintained contracture evoked by isotonic K Krebs solution induced further development of the contracture. However, on pre-treatment with thymol, neither excess Ca nor acetylcholine could evoke a mechanical response in isotonic K Krebs solution.6. The results obtained from the present experiments are discussed in relation to the roles of Ca on the smooth muscle cells.