Mechanical activity and force-frequency relationship of isolated mouse papillary muscle: effects of extracellular calcium concentration, temperature and contraction type.

Cardiac physiology of the mouse is becoming increasingly important because the mouse is the mammalian model animal of choice for genetic modifications. However, mouse cardiac muscle is still poorly characterized under physiological conditions and inconsistent results have been published in the literature regarding mechanical activity especially the force-frequency relationship in isolated mouse muscle preparations. In this study we investigated systematically several mechanical parameters of isolated mouse papillary muscle such as force-frequency relation, twitch force, time to peak tension, relaxation time and post-rest potentiation at different experimental conditions.

Effects of gastrin-releasing peptide (GRP) on the mechanical activity of the human ileocaecal region in vitro.

Mechanical activity was recorded in muscle preparations isolated from the human ileocaecal region. Gastrin-releasing peptide (GRP, 10(-9)-10(-7) mol L-1) produced two types of response in the different muscle layers. Longitudinally cut strips showed a concentration-dependent increase in the rhythmic activity, whereas the circularly orientated layers generally reacted with a small decrease in tone.

Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro.

Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (+/- 4% SEM, n = 15; 10(-6) M) of the histamine (10(-5) M) responses.

Electrical and chemical control of smooth muscle activity of rabbit corpus cavernosum in vitro.

Objectives: This study sought to further elucidate the regulation of cavernous smooth muscle tone and to characterize mechanisms of cavernous activation and relaxation.

Methods: In isolated strips of rabbit corpus cavernosum, extracellular electrical and mechanical activity were recorded simultaneously before and after pharmacologic stimulation.

Results: Spontaneous mechanical activity was characterized by fast phasic contractions (frequency 6 to 30 min-1) associated with fluctuations of the extracellular electrical signals.