Effect of Na+ pump suppression on reactivity of rat trachealis to cooling

Cooling-induced gastrointestinal smooth muscle contractions in the rat

The aim of this study was to assess the effect of cooling on smooth muscle contraction in various parts of the gastrointestinal tract (esophagus, stomach, duodenum, jejunum and colon) and to investigate the basic mechanism underlying cooling-induced (CIC) tonic and rhythmic contractions. Recordings of isometric tension from smooth muscle strips of different parts of the rat gastrointestinal tract were performed using organ-bath techniques, and stepwise cooling was applied. Cooling was tested before and after the addition of various standard agents interfering with known neurogenic (autonomic blockers, tetrodotoxin, capsaicin) and myogenic mechanisms of contraction (calcium channel blockers, Sarcoplasmatic and Ca2+-ATPase pump inhibitors). Step-wise cooling (37 degrees C to 5 degrees C) of all gastrointestinal smooth muscle preparations induced reproducible graded tonic contractions, inversely proportional to temperature. CIC was most pronounced in the jejunum. Cooling abolished rhythmic smooth muscle activity. CIC was not dependent on a neural mechanism nor the release of neurotransmitters, but linked to translocation of calcium. It was reduced by incubation in Ca2+-free solution. Blockage of the Ca2+-ATPase pump, which inhibits the extrusion of calcium, plays a significant role in the process and enhances CIC. Cooling of gastrointestinal smooth muscle preparations induces graded myogenic contractions inversely proportional to the temperature. The mechanism is not dependent on local nervous control but related to a temperature-sensitive process of calcium translocation.

Cooling-induced bladder contraction: studies on isolated detrusor muscle preparations in the rat

OBJECTIVES

Detrusor muscle contraction and uninhibited micturition after intravesical instillation of ice water is interpreted as a sign of upper motor neuron lesions. The basic mechanism of cooling-induced contraction (CIC) at the level of smooth muscle, however, has not been satisfactorily explained. We therefore designed model experiments with cooling of rat detrusor muscle.

METHODS

We recorded isometric tension from strips of rat urinary detrusor muscle in organ baths during stepwise cooling. CIC was tested before and after addition of various standard agents interfering with known neurogenic (autonomic blockers, tetrodotoxin, capsaicin) and myogenic mechanisms of contraction (calcium channel blockers).

RESULTS

Stepwise cooling (37 degrees to 5 degrees C) of detrusor muscle induced reproducible graded contractions, inversely proportional to temperature. CIC was not dependent on a neural mechanism (not blocked by tetrodotoxin or capsaicin) or the release of neurotransmitters but was linked to translocation of calcium. It was reduced by calcium channel blockers and Ca(2+)-free solution. Blockage of the Ca(2+)-adenosine triphosphatase pump, which inhibits the extrusion of calcium, also plays a significant role in the process and enhances CIC.

CONCLUSIONS

Cooling of detrusor muscle preparations induces a graded myogenic contraction inversely proportional to the temperature. The mechanism is not dependent on local nervous control but is related to calcium translocation.

Effect of temperature on muscarinic cholinoceptor-mediated phosphoinositide metabolism and tension generation in bovine tracheal smooth muscle

The effect of decreased temperature on phosphoinositide metabolism was studied in flurbiprofen pretreated bovine tracheal smooth muscle (BTSM) by investigating the consequences of cooling on muscarinic-cholinoceptor-mediated [3H]inositol phosphate ([3H]InsP) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) accumulation, basal phosphoinositidase C (PIC) activity and airways smooth muscle (ASM) tone. Cooling of [3H]Ins labelled BTSM slices from 37 degrees C to 27 degrees C for 20 min prior to the addition of agonist caused a substantial (73.0 +/- 2.5%) inhibition of carbachol (100 microM, 30 min)-stimulated [3H]InsP accumulation compared to values measured at 37 degrees C. The degree of inhibition of [3H]InsP accumulation was similar at all agonist time points (2-30 min) studied. In parallel experiments, cooling of unlabelled BTSM slices from 37 degrees C to 27 degrees C resulted in a 34% reduction in basal Ins(1,4,5)P3 mass (37 degrees C, 13.1 +/- 0.6 pmol mg-1 protein; 27 degrees C, 8.9 +/- 0.9 pmol mg-1 protein; P < 0.02) and markedly attenuated carbachol (100 microM)-stimulated increases in Ins(1,4,5)P3 accumulation. Basal PIC activity in the soluble fraction of BTSM homogenates, measured using a [3H]phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) /deoxycholate assay system, was also significantly lower at 27 degrees C compared to 37 degrees C (initial velocities of PtdIns(4,5)P2 hydrolysis of 853 +/- 167 (37 degrees C) and 418 +/- 119 (27 degrees C) pmol min-1 ml-1 (1/400 diluted) BTSM cytosol; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Hypothermia augments non-cholinergic neuronal bronchoconstriction in pithed guinea-pigs

Electrical stimulation at C4-C7 in the spinal canal of pithed guinea-pigs injected with atropine, d-tubocurarine and pentolinium caused frequency-dependent bronchoconstriction. Such non-cholinergic responses to electrical stimulation, unlike responses to substance P, were abolished by pretreatment with capsaicin but not by mepyramine or propranolol. Bronchoconstrictor responses to electrical stimulation were inversely related to rectal temperature (between 30-40 degrees C) whereas responses to substance P increased with increasing temperature over the same range. Ouabain (i.v.) augmented responses to electrical stimulation at 35-37 degrees C but depressed those at 30-32 degrees C. Both morphine and the alpha 2-adrenoceptor agonist B-HT920 (i.v.) inhibited non-cholinergic-mediated bronchoconstrictor responses at 30-32 degrees C. These results stress the importance of adequate control of body temperature in this preparation. Lowered body temperature may increase neuronal output of neuropeptides whilst depressing bronchial smooth muscle sensitivity. The data support previous conclusions regarding the role of Na+/K+ activated ATPase in temperature-induced changes in sensitivity to bronchoconstrictor stimuli.