Electrical and mechanical characteristics of vascular smooth muscle response to norepinephrine and isoproterenol

Effects of norepinephrine (NE) and isoproterenol on simultaneously recorded electrical and contractile activity in rat portal vein were studied using a sucrose-gaps technique. This vascular smooth muscle shows spontaneous phasic contractions correlated with bursts of action potentials. Norepinephrine (10 -9 9 to 10 -7 w/v) increases the duration of the bursts and shortens the interval between after an initial period of continuous spike discharge. The tension response is greater than can be accounted for by the increase in electrical activity. High NE concentrations (10-5) produce depolarization, decrease of spike amplitude, or even abolition of spikes and maintained contractions. Norepinephrine increases contracture tension of K + -depolarized portal vein without changing membrane potential. Electrical and mechanical activity is reinitiated in preparations inactivated by elimination of Ca 2+ this may be due to release of bound calcium. Phenoxybenzamine abolishes the above NE responses. The typical response to isoproterenol (10 9 to 10 7 ) in a normal ionic environment consists of moderate depolarization, decreased burst duration, but increased frequency of bursts and inhibition of tension development which is not simply correlated with the change in electrical activity. This pattern resembles that produced by lowering [Ca 2+ ] o . Contracture tension in high [K + ] o is reduced by isoproterenol without changes in membrane potential. These responses to isoproterenol are abolished by propranolol. At high concentrations of isoproterenol (10 -5 ) the inhibitory responses are not sustained, but revert to a pattern of activity resembling that induced by NE.

Influence of the ionic environment on spontaneous electrical and mechanical activity of the rat portal vein

The effects of variations in external K + and Ca 2+ concentrations on electrical and mechanical activity of the isolated rat portal vein were studied using a sucrose-gap technique. Spontaneous activity in normal Krebs solution consists of bursts of action potentials accompanied by phasic contractions. Moderate reduction in [K+] o results in slight hyperpolarization with decreased discharge frequency. Greater reduction or total removal of extracellular K causes a temporary increase in burst frequency. Graded increases in [K+] o from 6 up to 128 mM cause depolarization with an increase in discharge frequency and in contraction amplitude until [K+] o reaches a level of 6 to 7 times normal when spike potentials are abolished and a contracture develops. The relationship between membrance potential and log [K + ] o indicates a relatively low permeability to K + . Increasing [Ca 2+ ] o causes slight hyperpolarization, decreased burst frequency, increased burst duration and increased contraction amplitude. Reducing [Ca 2+ ] o causes increased frequency of discharge and shortening of bursts, until single spikes appear, each preceded by a prepotential; thus the activity resembles that in cardiac pacemaker cells. In Ca 2+ -free solution, electrical and mechanical activity ceases within 10 to 15 min. Calcium is essential for activation of the contractile mechanism and for maintenance of spontaneous spike discharge.

Impaired phytohaemagglutinin-induced cytotoxicity in vitro of lymphocytes from patients with Hodgkin's disease or chronic lymphatic leukaemia

Lymphocytes from healthy, unsensitized donors damage allogeneic tissue culture target cells in the presence of phytohaemagglutinin (PHA). In this investigation, blood lymphocytes from eleven patients with clinically active Hodgkin's disease and from eight patients with chronic lymphatic leukaemia (CLL) were tested in vitro for PHA-induced cytotoxicity to Chang cells. Blastoid transformation and DNA-synthesis in the presence of PHA were studied in parallel experiments. The cytotoxicity of the patients' lymphocytes was significantly lower than that of lymphocytes from healthy donors. Synthesis of DNA and blastoid transformation was subnormal in all cases of CLL and in most cases with Hodgkin's disease. A good correlation between cytotoxicity and stimulation by PHA was observed in most cases.

The incidence of positive skin reactions to tuberculin was high in the CLL-group and low in the Hodgkin group. If it is assumed that the pool of immunologically competent cells was normal in the CLL-patients, this would account for their intact cellular reactivity in vivo. In contrast, the high proportion of leukaemic cells could be expected to mask the reactivity of the normal CLL-lymphocytes in vitro. The weak in vitro reactivity of the lymphocytes in Hodgkin's disease is in line with the view that deficient lymphocytes are present in this disease and suggests that the patients' pool of immunologically competent cells is reduced. This could also contribute to the anergic state seen in these patients.

Contraction of vascular smooth muscle in response to plasma. Comparison with response to known vasoactive agents

Addition of plasma to the physiologic salt solution in which helical strips of vascular smooth muscle were suspended caused the muscle to contract. The plasma was obtained from dog arterial blood which, extracorporeally, had been in contact only with siliconized polyethylene in the cold. The strips were from large and small vessels from several sites in rabbit and dog. The contractions were reproducible and dose dependent. Threshold concentrations for contraction ranged from 2% to 30% depending on the source of the smooth muscle. In concentrations too low to produce contraction, plasma potentiated tension developed in response to stimulation by epinephrine, angiotensin, and KC1. The response of the strips to plasma was compared with their response to the several known vasoactive agents of plasma: epinephrine, norepinephrine, serotonin, angiotensin, vasopressin, bradykinin and histamine. Important differences were found. It is possible that in normal plasma there is an as yet undefined vasoactive component which in situ may play a role in the maintenance of vascular tone.