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Summary. When a frog's striated muscle (m. sartorius) is immersed in Ringer solution containing 2.5–10 × 10–4 w/v of the free base caffeine tension develops and the muscle contracts. The contracture is graded according to dose and reverses rapidly upon removal of the drug. Higher concentrations of caffeine produce an irreversible contracture. In a muscle immersed in isotonic K2SO4 or KCl solution caffeine produces exactly the same kind of muscle contracture as in a muscle kept in Ringer's fluid. Prolonged soaking (96 hours) of a muscle in isotonic K2SO4 solution does not reduce its responsiveness to caffeine. Local application of caffeine from a micropipette to a muscle fibre produces a localized contracture when the tip of the pipette is at the outer surface of the cell membrane. When the tip is inserted into the fibre no contracture is observed indicating that the caffeine action is confined to the muscle membrane. In concentrations helow 10‐3 w/v caffeine does not alter the resting meinhrane potential of iituscle fibres. Neither does the drug markedly reduce the transverse niuscle iiienibraiie resistance. It is suggested that caffeine at the niuscle membrane starts a process which activates the contractile mechanism in the interior of the fibre. This process is believed to be the same as that activated by the propagated action potential. The nature of the process (or processes) linking the membrane to the contractile elements is unknown hut the present results makes it unlikely that it is an electric current or potential change.

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. • Information about the electrophysiological properties of vascular smooth muscle and the relationship between electrical and mechanical activity will provide a basis for better understanding of the action of drugs on blood vessels. This paper mainly describes results obtained by simultaneous recordings of electrical and mechanical activity of the rat portal vein. This vessel was introduced as a suitable preparation for studying electrical activity of vascular smooth muscle by Funaki and Bohr (1) working with intracellular microelectrodes. A sucrose-gap technique has been used for recording electrical activity in the present investigation. The effects of changes in the external ionic environment on membrane potential, frequency and pattern of spike discharge, and tension development, and on the normal correlation of these parameters have been studied. Another paper deals more specifically with the actions of drugs.Results pertaining to the current study have been presented in preliminary form (2, 3).

This is the second study to find the prevalence of seasonal affective disorder and subsyndromal seasonal affective disorder to be lower among Icelanders or their descendants than among populations along the east coast of the United States. The results indicate that the relationship between prevalence of these disorders and geographic latitude is more complex than has previously been suggested; genetic adaptation in Icelandic populations may play an important role.

The effect of external ATP and related compounds on the electrical and mechanical activity of isolated pieces of taenia coli has been studied. ATP, AMP and adenosine caused a decrease in the spontaneous tone, a decrease in the frequency of spike discharge, and hyperpolarization. ATP was up to 100 times as potent an inhibitor of spontaneous activity as AMP or adenosine. GMP, guanosine and inosine had no effect. High K+ contractures were relaxed by the same compounds and adenine, which was the most potent. Here again GMP, guanosine and inosine had no effect. ATP, AMP and adenosine prevented or shortened the initial depolarization produced by acetylcholine and carbachol. Inorganic phosphate was liberated from ATP and AMP applied to the bathing solution. The hydrolysis was not significantly decreased by g‐strophanthin. p‐Hydroxy‐mercuribenzoate caused an initial excitation as well as g‐strophanthin but neither inhibited the relaxing effect of ATP. The effects of extracellularly applied ATP are consistent with the view that they are exerted through changes in membrane permeabilities and that some of these effects are brought about by the adenosine part of the molecule.