After 30 min carbachol stimulation, tonic contraction
was reduced by isoprenaline more significantly on the detrusor strips isolated from Gegen 300-treated rats (Fig.
The tonic contraction
prevents gastroesophageal reflux even at times of increased intra-abdominal pressure.
Phasic contractions result from a transient increase in cytosolic-free [Ca.sup.2+] concentrations, whereas during tonic contractions
the initial peak [Ca.sup.2+] concentration does not return to baseline but reverts to a sustained lower level .
Phasic smooth muscle has several active states: tonic contraction
, tonic relaxation, and rhythmic contractions.
In the neonatal period and early infancy, apnea, tonic contraction
of the trunk and circular movements in the extremities may be observed (9).
In the resting state, the CP muscle is under tonic contraction
and relaxes only momentarily during swallowing, belching, or vomiting.
Transmembrane mobility of [Na.sup.+) and [Ca.sup.2+] ions and more specifically, the increase of cytoplasmic calcium concentration are responsible for tonic contraction
in smooth muscle.
(1) A rapid flexor spasm occurs in the form of involving neck, trunk and limbs followed by tonic contraction
sustained for 2-10 seconds.
To evaluate the involvement of potassium ([K.sup.+]) channels, tetraethylammonium (TEA; a non-selective potassium channel blocker, 10 [micro]M), barium chloride (a [K.sub.ATP] blocker, 100 [micro]M) or glibenclamide (a [K.sub.ATP] blocker, 10 [micro]M) were applied to rat vessel rings, 10 min prior to the contraction by NA (1 [micro]M) followed by addition of TAAC (100 [micro]M) during the resulting tonic contraction
. The responses were compared with those obtained in vessels that had not been treated with these inhibitors.