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Biomedical subjects

I C Smith

Publications and source records attributed to I C Smith.

At least 253 records · Page 14Linked to original sources
PubMed1972

Energetics of activation in frog and toad muscle.

1. If activation heat reflects the operation of the calcium pump it should be independent of actomyosin activity. The semitendinosus preparation affords a technique for removing actomyosin activity since the muscle can be stretched till there is almost no overlap between the filaments.2. Heat production, H, in twitches and tetani of stretched muscle fits the relation H = A+M.P/P(ot) where P/P(ot) is the fraction of the optimal tension remaining at the stretched length and A and M are assumed to be the activation dependent and actomyosin dependent heat components.3. For twitches the A component is early and fast and constitutes 0.26 (S.D. 0.09) of the heat production at normal muscle lengths. Its time course is similar in both frog and toad muscle although both M and P are twofold slower in toad muscle. High concentrations of CO(2) slow only M and P(ot). The A component is associated with a normal recovery heat.4. The twitch-tetanus tension ratio, after correction for the extra shortening that occurs during a tetanus, does not vary with the degree of muscle stretch: it is thus probable that twitch activation does not vary with muscle stretch.5. Moderately hypertonic Ringer solution reduces M and P(ot) but not A, but strongly hypertonic solution also reduces A. Zn(2+), No(3) (-) and second shock potentiation of a twitch increase A, M and P(ot) in proportion to each other.

Action Potentials↗
PubMed1971

The mechanical and thermal properties of frog slow muscle fibres.

1. A study has been made of the mechanical behaviour and the heat production of frog slow muscle fibres in iliofibularis nerve-muscle preparations at 20 degrees C.2. The slow fibre isometric tension and its rate of development increase with stimulation frequency, the increases beyond 30 Hz being relatively small. Relaxation rate also increases with stimulation frequency. The tension-length curve and maximum isometric tension (250 mN.mm(-2)) are similar to those of twitch fibres. The maximum shortening velocity is estimated to be 0.11 tonus bundle lengths per second.3. For contractions up to 60 sec at 30-50 Hz the slow fibre heat rate is steady at 6 mJ.g(-1).sec(-1). Slow fibres produce aerobic recovery heat with a time course similar to that of twitch fibres.4. The accuracy of the results is discussed, and a comparison is made with the properties of twitch fibres. It is concluded that the tension-producing reactions are thirty times slower in the slow fibres.

Animals↗