Carbonic anhydrase and osteoclasts: localization by labeled inhibitor autoradiography.

Autoradiography with tritiated acetazolamide indicates that osteoclasts of the hen and chick contain concentrations of carbonic anhydrase which are similar to those in pancreatic acinar cells. Grain counts of osteoblasts and osteocytes were not different from background. Thus, a sufficient quantity of carbonic anhydrase seems to be present in osteoclasts to be of physiological importance in bone resorption.

Changes in blood flow to bones during the hypocalcemic and hypercalcemic phases of the response to parathyroid hormone.

Labeled microspheres were used to measure blood flow to the leg bones of the laying hen at 0, 3, and 30 min after iv injection of parathyroid hormone (PTH) (Wilson) or the synthetic 1 to 34 fragment of bovine parathyroid hormone (PTH 1-34). At 3 min, which corresponds to the hypocalcemic phase of the PTH response, blood flow to the combined femur, tibia, and metatarus was significantly reduced by PTH (Wilson) relative to 0 time and to carrier-injected controls. At 30 min, i.e., the time of maximum hypercalcemia in the hen, blood flow to these bones was significantly increased relative to 0 time. The results obtained with PTH 1-34 were similar, except that the decrease at 3 min was only significant in comparison with the controls injected with inactivated hormone. Femoral blood flow and the venous minus arterial calcium gradients across the femur were positively correlated, irrespective of sampling time (0 or 30 min) or type of injection (PTH [Wilson] or carrier). Taken together, these results suggest that there is a relationship between calcium mobilization from bone and the rate of osseous blood flow. Other organs which showed significant changes in blood flow after PTH (Wilson) were the adrenals, thyroids, and shell gland; the cerebellum, parathyroids, heart, spleen, liver, pancreas, duodenum, magnum, isthmus, and kidneys were not affected.

A study of light-initiated currents in Limulus lateral eye retinular cells.

Light-initiated currents in Limulus lateral eye retinular cells were studied using the voltage clamp technique. To assess the validity of such current measurements, the isopotentiality of retinular cells was determined on triply impaled cells and the effect of voltage clamping one retinular cell on adjacent retinular cells and on the eccentric cell in the same ommatidium was determined. The results of the experiments are: (1) retinular cells are isopotential at loci 100 micron apart; (2) appreciable steady state current during the clamping episodes leaks into neighboring retinular cells and the eccentric cell; (3) light-initiated currents exhibit two components; (4) there is a dynamic change in the resistance of the photoreceptor membrane during development of the receptor potential; (5) suppression of the rising phase (C1) of the receptor potential does not affect subsequent voltage changes; (6) suppression of the sodium influx which normally produces C1 has only minor effects on subsequent voltage changes; (7) reduced [KC1]out increases and increased [CK1]out decreases the reversal potential of light-initiated currents; and (8) reduced [NaC1]out reduces the magnitude and the reversal potential of light-initiated currents.

Partial voltage clamping of Limulus ventral photoreceptor potentials: evidence of programmed conductance changes.

Light-initiated currents elicited by brief light stimuli from Limulus ventral photoreceptors bathed in normal sea water generally exhibit a smooth contour, although the unclamped receptor potential elicited by an identical light stimulus usually exhibits distinct C1 and C2 components. However, light-initiated currents obtained from cells exposed to chlorobutanol often exhibit two components. Data from such experiments indicate that peak C2 current is more strongly voltage dependent than peak C1 current, as in Limulus lateral eye retinular cells. The results of partial voltage clamp experiments with ventral photoreceptors in which the clamping episode terminated at different times during the receptor potential reveal relatively minor perturbations of the rebound receptor potential when compared with the unclamped control response. These findings suggest that the temporal pattern of the membrane conductance changes which underlie the receptor potential is determined prior to the occurrence of the receptor potential. It is likely that the program for these conductance changes is developed during the latent period of the receptor potential.

Two latent period processes in Limulus ventral photoreceptors.

The latent period of Limulus ventral photoreceptor potentials consists of two contiguous time segments, S1 and S2, which exhibit the following properties: (1) the duration of S1 is inversely dependent on the incident energy provided by the first stimulating light flash; (2) the duration of S1 is prolonged in the presence of GTP-gamma-S [guanosine-5'-0- (3-thiotriphosphate)] or papaverine; (3) the duration of S1 is abbreviated in the presence of sodium vanadate or chlorobutanol; (4) the duration of S2 is abbreviated by light adaptation; and (5) the duration of S2 is prolonged more than S1 in a low temperature environment. The existence of these two components of the Limulus ventral photoreceptor potential latent period is demonstrable both in dark adapted photoreceptors, using single constant intensity light pulses of varying duration, or in partially light adapted photoreceptors, using a stimulating conditioning pulse-test pulse sequence. On the basis of these results it is tentatively concluded that the two segments of the latent period of Limulus ventral photoreceptor potentials are occupied by different processes. The first process, occupying the S1 segment, generates a critical concentration of a photoproduct which, directly or indirectly, eventually alters the conductance of the active photoreceptor membrane. The second process, occupying the S2 segment, is concerned with the initiation of the SPFs which sum to produce the receptor potential. It is possible that the hydrolysis of GTP actively participates in the first process.

Temporal relationships of latency and magnitudes of Limulus ventral photoreceptor potentials elicited by two light pulses.

As the dark interval between two stimulating light pulses increases, the latent period of the ensuing receptor potential increases to an asymptote reached about midway during the latency and is, thereafter, constant. The latent period is thus divisible into two segments, the first of which is light sensitive and the second not. The possible significance of these segments has been explored [12]. During the time the latent period is increasing toward its limiting value, the magnitudes of both components of the receptor potential are constant and maximal. The magnitude of the first component of the receptor potential begins to decline at a pulse interval of 15 msec, signify that the contribution of photons incident on the photoreceptor from the second pulse is diminishing. The magnitude of the second component of the receptor potential begins to decline at a pulse interval of 20 msec, suggesting that the contribution of photons delivered by the first pulse is diminishing. These results demonstrate that the two pulse stimulating paradigm reveals two segments of the receptor potential latent period and the ability of the photoreceptor to integrate radiant energy incident during the latent period, as measured by receptor potential magnitude.

Automated computerized rat eater meter: description and application.

A real-time Automated Computerized Rat Eater Meter was developed by modifying commercially available metabolic cages. Food access via a feeding tunnel was monitored by photocells. Food consumption was measured by an electronic scale. The signals thus generated were processed by a computer. This allowed us to continuously measure the spontaneous feeding behavior of free-feeding nondeprived Fischer rats for a sum total of 35 study days. Based on our data, we defined a meal as an episode of food consumption preceded and followed by at least 5 minutes of no feeding. Fischer rats showed periodic nychthemeral eating behavior. Food consumption, number of meals, meal sniffs, intermeal sniffs, and, consequently, eating activity were greater during the dark cycle than the light cycle. Meal duration, meal size, and thus food consumption rates remained constant throughout both cycles. Our modification of commercially available metabolic cages provides unique data for continuously monitoring rat feeding patterns over prolonged periods of time.

A limited restraint harness for use in long-term infusion of chickens.

A limited restraint harness was developed which permits long-term infusion of chickens under near normal conditions. The harness allows the birds to stand, sit, move forward and backward, and turn 180 degrees in either direction without twisting the cannula.

Gravitropism in Higher Plant Shoots : II. Dimensional and Pressure Changes during Stem Bending.

Dimensional changes during gravitropic bending of cocklebur (Xanthium strumarium L.) dicot stems were measured using techniques of stereo photogrammetry. The differential growth is from an increased growth rate on the bottom of the stem and a stopping or contraction of the top.Contraction of the top was especially evident upon release and immediate bending of horizontal stems that had been restrained between stiff wires for 36 hours. The energy for this could have been stored in both the top and bottom, since the bottom elongated, and the top contracted.Forces developed during bending were measured by fastening a stem tip to the end of a bar with attached strain gauges and recording electrical output from the strain gauges. Restrained mature cocklebur stems continued to accumulate potential energy for bending for about 120 hours, after which the recorded force reached a maximum.Pressures within castor bean (Ricinus communis L.) stems were also measured with 3.5-millimeter diameter pressure transducers. As expected, the pressure on the bottom of the restrained plants increased with time; pressures decreased in vertical controls, tops of restrained stems, and bottoms of free-bending stems. Pressures increased in tops of free-bending stems. When restrained plants were released, pressure on the bottom decreased and pressure on the top increased. Results suggest a possible role for cell contraction in the top of stems bending upward in response to gravity.

Regulation of calcium appetite in broiler chickens.

The regulation of the appetite for calcium was studied in broiler chickens which had been trained to meet their calcium requirement by consuming a calcium supplement (10% Ca) provided separately from a calcium-deficient feed (0.12% Ca). Calcium supplement intake was reduced within 150 minutes after intravenous injection of 60 U/kg parathyroid hormone or continuous infusion of 0.077 mg/minute calcium into one common carotid artery. Supplement consumption was also depressed during the first 8 days of continuous infusion of 1 U/kg/hour parathyroid hormone; after 8 days the birds became refractory. Continuous infusion of 0.2 Medical Research Council (MRC) units/kg salmon calcitonin for 10 days or daily intramuscular injections of 1 mg/kg testosterone propionate and 2 mg/kg estradiol dipropionate for 12 days, either alone or in combination, had no effect on calcium appetite. It is concluded that the calcium appetite may be inhibited by increased concentrations of ionic calcium in blood and that the change in behavior is sufficiently rapid to play a role in the calcium homeostasis of birds.

A mathematical model of parasystole and its application to clinical arrhythmias.

A ventricular parasystolic focus capable of generating manifest ectopic beats should not be totally insulated from the electrical events that accompany depolarization in the surrounding tissue; the intrinsic cycle length of the ectopic discharge may be modulated by electrotonic influences transmitted across the zone of "protection." To study the nature of the interaction, response patterns were examined in a mathematical model programmed to simulate an ectopic pacemaker protected, but not divorced from ventricular responses to the normal pacemaker. Computer runs covered a wide range of heart rates, and a wide range of magnitudes of the simulated electrotonic influence. Application of the results obtained in the model to published examples of complex arrhythmias revealed a remarkably close fit to many clinical examples. This findings suggests that many patterns attributed to a re-entrant "extrasystolic" rhythm may, in fact, represent the modulated activity of a parasystolic focus.