The effect of Community Based Education and Service (COBES) on medical graduates' choice of specialty and willingness to work in rural communities in Ghana.

BACKGROUND: Career choices and placements of healthcare professionals in rural areas are a major problem worldwide, and their recruitment and retention to these areas have become a challenge to the health sector. The purpose of this study was to investigate the effect of Community Based Education and Service (COBES) on medical graduates' choice of specialty and willingness to work in a rural area. METHOD: This cross sectional survey was conducted among 56 pioneering graduates that followed a Problem Based Learning/Community Based Education and Service (PBL/COBES) curriculum. Using a mixed methods approach, open-and closed-ended questionnaire was administered to 56 graduates. Cross tabulation using Chi-square test were used to compare findings of the quantitative data. All qualitative data analysis was performed using the principles of primary, secondary and tertiary coding. RESULTS: All 56 graduates answered and returned the questionnaire giving a 100 % response rate. 57.1 % (32) of them were male. Majority of them lived in towns (41.1 %) and cities (50 %) prior to medical school. A significant number of graduates (53.6 %,) from the cities, without any female or male predominance said COBES had influenced their choice of specialty. Again, a significant proportion of graduates from the towns (60.9 %,) and cities (67.8 %,), indicated that COBES had influenced them to work in the rural area. However, there was no significant difference between males and females from the towns and cities regarding the influence of COBES to work in the rural area. Qualitative data supported the finding that COBES will influence graduates willingness to work in the rural area CONCLUSION: The majority of graduates from the towns and cities in Ghana, with a male predominance, indicated that COBES may have influenced their choice of specialty and willingness to practice in the rural areas despite their town or city based upbringing.

Extracellular ATP activates ERK1/ERK2 via a metabotropic P2Y1 receptor in a Ca2+ independent manner in differentiated human skeletal muscle cells.

ATP is released at the neuromuscular junction to regulate development and proliferation. The sequential expression of P2X and P2Y receptors has been correlated to these effects in many species and cell lines. We have therefore investigated ATP mediated signalling in differentiated primary human skeletal muscle cells. ATP was capable to trigger Ca2+ transients in these cells via P2Y receptors which were not attributable to Ca2+ influx via P2X receptors. Instead, ATP propagated the formation of inositol phosphate (IP) with an EC50 of 21.3 microM. The Ca2+ transient provoked by ATP was abrogated roughly 75% by the phospholipase C (PLC) inhibitor, U73122. Interestingly, the ryanodine sensitive Ca2+ pool was not involved in ATP triggered Ca2+ release. On mRNA level and by a pharmacological approach we confirmed the presence of the P2Y1, P2Y2, P2Y4 and P2Y6 receptors. Substantially, ATP activated IP formation via a P2Y1 receptor. In addition, ATP elicited extracellular signal regulated kinase (ERK)1/2 phosphorylation in a time and concentration dependent manner, again mainly via P2Y1 receptors. The ATP mediated ERK1/2 phosphorylation was strictly dependent on phospholipase C and PI3 kinase activity. Importantly, ATP mediated ERK1/2 phosphorylation was Ca2+ independent. This observation was corroborated by the finding that conventional protein kinase C inhibitors did not suppress ATP triggered ERK1/2 phosphorylation. Taken together, these observations highlight the importance of ATP as a co-neurotransmitter at the neuromuscular junction via dual signalling, i.e. IP3 receptor mediated Ca2+ transients and Ca2+ insensitive phosphorylation of ERK1/2.

Use-dependent inhibition of the skeletal muscle ryanodine receptor by the suramin analogue NF676.

The skeletal muscle Ca2+ release channel, the ryanodine receptor, is activated by the trypanocidal drug suramin via the calmodulin-binding site. As calmodulin activates and inhibits the ryanodine receptor depending on whether Ca2+ is absent or present, suramin analogues were screened for inhibition of the ryanodine receptor. Up to 300 microM, the novel suramin analogue, 4,4'-(carbonyl-bis(imino-4,1-phenylene-(2,5-benzimidazolylene)carbonylimino))-bis-benzenesulfonic acid disodium salt (NF676) was not able to significantly inhibit the basal [3H]ryanodine binding. However, kinetic analysis of the high affinity [3H]ryanodine binding elucidates a time-dependent increment of inhibition by NF676, which is indicative for an open channel blocker. Moreover, the ryanodine receptor was much more sensitive towards inhibition by NF676 when preactivated with caffeine or the nonhydrolysable ATP analogue, adenylyl-imidodiphosphate. Nonetheless, the suramin activated ryanodine receptor was not susceptible towards high-affinity NF676 inhibition, indicating an allosteric hindrance between the binding sites of suramin and NF676. In the line of this finding, NF676 per se was not capable to elute the purified ryanodine receptor from a calmodulin-Sepharose, but it prevented the elution by suramin. Other than suramin, NF676 did not inhibit the Ca2+ ATPase of the sarcoplasmic reticulum. However, suramin-induced Ca2+ release from sarcoplasmic reticulum was completely abrogated by preincubation with NF676. Taken together, we conclude from these data that NF676 represents a novel lead compound as a potent use-dependent blocker of the skeletal muscle ryanodine receptor via an allosteric interaction with the suramin-binding site.

Store operated Ca2+ influx by selective depletion of ryanodine sensitive Ca2+ pools in primary human skeletal muscle cells.

The contraction and relaxation of skeletal muscle is driven by release of Ca2+ from sarcoplasmic reticulum through the ryanodine receptor type 1 and extruding the ion from the cytosol by Ca2+ ATPases. Efficient refilling of the empty Ca2+ stores is essential for repetitive cycles of muscle contraction and relaxation, but not investigated in human skeletal muscle cells. Here we show that under conditions of selective depletion of the ryanodine-sensitive Ca2+ pool Ca2+ influx occurs in differentiated human skeletal muscle cells using the Ca2+ imaging technique. This Ca2+ influx is not due to permeation through the L-type Ca2+ channel and not observed under conditions of inhibited Ca2+ ATPase. The Ca2+ influx was visualised by quenching the intracellular fura2 signal with Mn2+ on single cell level and also using fluorescence photometry of cell suspensions. The Mn2+ influx was inhibited by the Ca2+ channel blockers La(3+) and SKF96356. The delineation of the signalling cascade leading to Ca2+ influx evoked by selective depletion of ryanodine sensitive Ca2+ stores showed that phospholipase C or protein kinase C were not involved. Interestingly, a Mn2+ influx was triggered by the cell-permeant analogue of diacylglycerol and further augmented by the application of RHC80267, a diacylglycerol lipase inhibitor. This signalling pathway could be attributed to the participation of a protein kinase C activity. However, Mn2+ influx evoked by selective depletion of ryanodine sensitive Ca2+ stores was not altered by RHC80267 or protein kinase C inhibitors. Using RT-PCR, correctly spliced mRNA fragments were detected corresponding to human transient receptor potential (TRPC) Ca2+ channels type 1, 3, 4 and 6. These data show that in skeletal muscle at least two independent mechanisms of Ca2+ influx exist. For Ca2+ influx triggered by the selective depletion of ryanodine sensitive Ca2+ stores we propose a phospholipase C independent coupling of ryanodine receptors to voltage insensitive Ca2+ channels.