The present study investigated the effects of gender on intracellular [Ca2+] ([Ca2+]i) in freshly isolated rat cardiac myocytes. Changes in [Ca2+]i in response to varied extracellular [Ca2+], different stimulus frequencies and addition of caffeine and isoprenaline were monitored using fura-2 in both male and female cardiac myocytes. Increasing extracellular [Ca2+] and stimulus frequency resulted in significant increases in peak [Ca2+] and the amplitude of the Ca2+ transient in both male and female cardiac myocytes. However, as extracellular [Ca2+] was raised, peak [Ca2+] and the amplitude of the Ca2+ transient increased significantly more in male than female cardiac myocytes. In addition a significant difference between male and female cells at each stimulus frequency was apparent. The time course of decay of the Ca2+ transient was significantly slower in female cardiac myocytes when compared with male cardiac myocytes, along with significantly slowed times to peak shortening and 50% relaxation, and a reduced extent of shortening. There was no significant difference in the amplitude of caffeine-induced [Ca2+]i responses between male and female cells, however, [Ca2+]i increased more readily in male cells than in female cells when isoprenaline was added. The data demonstrate that, under a variety of conditions, intracellular [Ca2+] rises to higher levels in cardiac myocytes from male as compared to female rats.

BackgroundWeb-based digital repositories allow educational resources to be accessed efficiently and conveniently from diverse geographic locations, hold a variety of resource formats, enable interactive learning, and facilitate targeted access for the user. Unlike some other learning management systems (LMS), resources can be retrieved through search engines and meta-tagged labels, and content can be streamed, which is particularly useful for multimedia resources.ObjectiveThe aim of this study was to examine usage and user experiences of an online learning repository (Physeek) in a population of physiotherapy students. The secondary aim of this project was to examine how students prefer to access resources and which resources they find most helpful.MethodsThe following data were examined using an audit of the repository server: (1) number of online resources accessed per day in 2010, (2) number of each type of resource accessed, (3) number of resources accessed during business hours (9 am to 5 pm) and outside business hours (years 1-4), (4) session length of each log-on (years 1-4), and (5) video quality (bit rate) of each video accessed. An online questionnaire and 3 focus groups assessed student feedback and self-reported experiences of Physeek.ResultsStudents preferred the support provided by Physeek to other sources of educational material primarily because of its efficiency. Peak usage commonly occurred at times of increased academic need (ie, examination times). Students perceived online repositories as a potential tool to support lifelong learning and health care delivery.ConclusionsThe results of this study indicate that today’s health professional students welcome the benefits of online learning resources because of their convenience and usability. This represents a transition away from traditional learning styles and toward technological learning support and may indicate a growing link between social immersions in Internet-based connections and learning styles. The true potential for Web-based resources to support student learning is as yet unknown.

1. The present study investigated the effects of ovariectomy (OVX) and 17beta-oestradiol replacement on [Ca2+]i in rat freshly isolated cardiac myocytes. 2. Myocytes were isolated from the hearts of sham, OVX and OVX + 17beta-oestradiol-replaced female rats by enzymatic digestion with collagenase. Changes in [Ca2+]i in response to varied extracellular [Ca2+] were measured using the Ca2+-sensitive dye fura-2, with the contractile responses of each cell measured as cell shortening. 3. Increasing extracellular [Ca2+] resulted in increased [Ca2+]i in all three groups. Peak [Ca2+]i and the amplitude of the Ca2+ transient were significantly greater (P < 0.01) in cells from OVX animals compared with cells from both sham and 17beta-oestradiol-replaced OVX animals. 4. The time-course of decay of the Ca2+ transient was significantly faster (P < 0.02) in OVX cells compared with both sham and 17beta-oestradiol-replaced cells. In addition, time to 50% relaxation was significantly faster (P < 0.04) and extent of shortening significantly greater (P < 0.01) in OVX cells than in either sham or 17beta-oestradiol cells. 5. These data demonstrate clear differences in peak [Ca2+]i and the amplitude of the Ca2+ transient between OVX female rat cardiac myocytes compared with intact and 17beta-oestradiol-replaced OVX female rat cardiac myocytes. This suggests that oestrogen may play a long-term role in limiting Ca2+ entry into the cardiac myocyte.

The mechanical and energetic consequences of long-term pressure-overload (POL) hypertrophy have been investigated in rabbits and compared with sham-operated controls (SOC). Hypertrophy was induced by banding the pulmonary artery of young rabbits and examining the mechanical, biochemical, and energetic properties of the compensated heart 10-16 wk later. Experiments were undertaken on papillary muscles from the hypertrophic hearts. At 27 degrees C and a stimulus frequency of 1 Hz there was a modest depression of peak stress development but no significant changes in isometric rise times and one-half widths or in isotonic maximum velocity of shortening and power output. The inverse relationship between peak stress and cross-sectional area (CSA) was practically identical in the POL and SOC groups. Both polarographic and myothermic investigations were made on papillary muscles. Hypertrophy nearly halved basal metabolism, and in isometric contractions there was increased isometric economy due to a combination of a lower stress cost and a reduced activation heat. Hypertrophy did significantly depress the extent of shortening leading to a reduced work output per beat. In isotonic contractions the reduced work output was offset by a reduced energy output such that there was no significant change in suprabasal mechanical efficiency. Biochemical studies showed that the transition of myosin isoenzymes to the V3 form was essentially complete in the POL group, but that the SOC group was also predominantly V3 when the animals were killed. There was a significant 30% decline in the Ca2(+)-stimulated adenosinetriphosphatase activity of the sarcoplasmic reticulum. It is concluded that in long-term compensated hypertrophy of rabbit hearts there are only a few mechanical and energetic differences between control and hypertrophic muscles. The changes that can be detected appear to predominantly reflect disturbances in cellular Ca2+ regulation.

The mechanical and energetic consequences of long-term volume-overload (VOL) hypertrophy have been investigated in rabbits and compared with the consequence in sham-operated controls (SOC). Hypertrophy was induced by creating an aortocaval shunt, and the mechanical, biochemical, and energetic properties of the compensated heart were examined approximately 12 wk later. At 27 degrees C and a stimulus frequency of 1 Hz there were no significant changes in peak stress development, 10-90% rise times, shortening velocity, work, and mechanical power output. There was, however, a prolongation of contractile duration. The inverse relationship between peak stress and cross-sectional area was unchanged in the VOL and SOC groups. Polarographic and myothermic experiments were made on papillary muscles. Hypertrophy produced a small increment in basal metabolism. In isometric studies there were no significant changes in either the activation heat magnitude or the slope of the heat-stress relationship. In isotonic contractions there was no change in work output or total enthalpy (heat + work), and as a result mechanical efficiency was unchanged. A force-length-area (FLA) analysis of the isotonic data showed no significant change in intercept or FLA contractile efficiency. Biochemical studies showed no significant difference in the myosin isoenzyme profile at the time of death. The Ca(2+)-stimulated adenosinetriphosphatase activity of the sarcoplasmic reticulum was unchanged as were the enzymatic activities of mitochondrial citrate synthase and alpha-ketoglutarate dehydrogenase. Interestingly essentially the same data were obtained from the hearts of four animals in failure and from the hearts of seven compensated animals.(ABSTRACT TRUNCATED AT 250 WORDS)