Cyclic adenosine monophosphate dependent and independent phosphorylation of sarcolemma membrane proteins in perfused rat heart.

This study was initiated in order to elaborate further on the mechanism by which epinephrine modulates cardiac function via protein phosphorylation. A membrane fraction has been isolated from freeze-clamped perfused rat heart that contains two phosphoproteins. These proteins have molecular weights of 36,000 (A protein) and 27,000 (B protein). The phosphorylation of the A protein occurs during the equilibration of the heart with inorganic [32P]phosphate. The phosphorylation of the B protein occurs in response to epinephrine. The A and B proteins are apparently identical with two phosphoproteins in enriched preparations of sarcolemma. The protein of the sarcolemma preparation equivalent to the A protein is phosphorylated in vitro by both cAMP-independent and cAMP-dependent protein kinases. The phosphorylation of the protein of the sarcolemma preparation equivalent to the B protein is catalyzed by the cAMP-dependent protein kinase. Thus the patterns of phosphorylation of these proteins in vivo and in vitro are compatible. The phosphorylation of the B protein has been documented in vitro to modulate calcium transport (Will, H., et al. (1973) Acta Biol. Med. Ger. 31, 45-52), but the response to epinephrine in the perfused heart is not apparently coordinated with the catecholamine-induced inotropic effect.     

Commentary: The ecological and evolutionary implications of allometry

Evolutionary Ecology - Allometry—the study of proportional growth of body parts, and the relationship of body size to an organism’s morphology, physiology and behaviour—is a...     

Internal carotid and vertebral arterial flow velocity in men at high altitude

Cerebral blood flow increases at high altitude, but the mechanism of the increase and its role in adaptation to high altitude are unclear. We hypothesized that the hypoxemia at high altitude would increase cerebral blood flow, which would in turn defend O2 delivery to the brain. Noninvasive Doppler ultrasound was used to measure the flow velocities in the internal carotid and the vertebral arteries in six healthy male subjects. Within 2-4 h of arrival on Pikes Peak (4,300 m), velocities in both arteries were slightly and not significantly increased above sea-level values. By 18-44 h a peak increase of 20% was observed (combined P less than 0.025). Subsequently (days 4-12) velocities declined to values similar to those at sea level. At altitude the lowest arterial O2 saturation (SaO2) and the highest end-tidal PCO2 was observed on arrival. By day 4 and thereafter, when the flow velocities had returned toward sea-level values, hemoglobin concentration and SaO2 were increased over initial high-altitude values such that calculated O2 transport values were even higher than those at sea level. Although the cause of the failure for cerebral flow velocity to increase on arrival is not understood, the subsequent increase may act to defend brain O2 transport. With further increase in hemoglobin and SaO2 over time at high altitude, flow velocity returned to sea-level values.     

Variation in cross‐sectional horn shape within and among rhinoceros beetle species

Sexual selection has equipped male rhinoceros beetles with large horns on their head and prothorax to aid in battle over access to females. Horns are used to pry and dislodge opponents from resource sites that attract females, so an optimal horn should be able both to withstand the high stresses imposed during fights, and to resist deflection in response to these loads. We examined the cross‐sectional morphology of horns using micro‐computed tomography scanning to determine how horn structure changes with horn length to withstand the different fighting loads. Specifically, we measured the second moment of area of horns within and among rhinoceros beetle species to assess whether changes in cross‐sectional morphology accompany changes in body size in order to maintain high strength and stiffness during fights. We find that the second moment of area of horns increases with body size both intra‐specifically and inter‐specifically, and that these relationships closely fit those predicted if horns have been selected to be strong and stiff fighting structures. Our results therefore support the hypothesis that rhinoceros beetle horns are structurally adapted for combat.