On the origin of rhythmic calcium transients in the ICC-MP of the mouse small intestine

Interstitial cells of Cajal associated with the myenteric plexus (ICC-MP) are pacemaker cells of the small intestine, producing the characteristic omnipresent electrical slow waves, which orchestrate peristaltic motor activity and are associated with rhythmic intracellular calcium oscillations. Our objective was to elucidate the origins of the calcium transients. We hypothesized that calcium oscillations in the ICC-MP are primarily regulated by the sarcoplasmic reticulum (SR) calcium release system. With the use of calcium imaging, study of the effect of T-type calcium channel blocker mibefradil revealed that T-type channels did not play a major role in generating the calcium transients. 2-Aminoethoxydiphenyl borate, an inositol 1,4,5 trisphosphate receptor (IP(3)R) inhibitor, and U73122, a phospholipase C inhibitor, both drastically decreased the frequency of calcium oscillations, suggesting a major role of IP(3) and IP(3)-induced calcium release from the SR. Immunohistochemistry proved the expression of IP(3)R type I (IP(3)R-I), but not type II (IP(3)R-II) and type III (IP(3)R-III) in ICC-MP, indicating the involvement of the IP(3)R-I subtype in calcium release from the SR. Cyclopiazonic acid, a SR/endoplasmic reticulum calcium ATPase pump inhibitor, strongly reduced or abolished calcium oscillations. The Na-Ca exchanger (NCX) in reverse mode is likely involved in refilling the SR because the NCX inhibitor KB-R7943 markedly reduced the frequency of calcium oscillations. Immunohistochemistry revealed 100% colocalization of NCX and c-Kit in ICC-MP. Testing a mitochondrial NCX inhibitor, we were unable to show an essential role for mitochondria in regulating calcium oscillations in the ICC-MP. In summary, ongoing IP(3) synthesis and IP(3)-induced calcium release from the SR, via the IP(3)R-I, are the major drivers of the calcium transients associated with ICC pacemaker activity. This suggests that a biochemical clock intrinsic to ICC determines the pacemaker frequency, which is likely directly linked to kinetics of the IP(3)-activated SR calcium channel and IP(3) metabolism.     

Biomonitoring with the BuzzardButeo buteo in the Netherlands: Heavy metals and sources of variation

The feasibility of using Buzzards found dead as indicators of environmental contamination was tested. Liver, kidney, and tibia specimens were examined for the presence of Cd, Cu, Pb, Mn, and Fe, which were used as markers. All buzzards submitted to the Veterinary Institute in 1992 were examined for cause of death and condition. Results showed that more than half had been poisoned or shot. As the condition of the birds worsened, fat reserves were depleted before protein reserves. Concentrations of the heavy metals rose in liver and kidney as nutrient reserves fell. Since the content of heavy metal per organ was not related to body condition, content was considered a better measure for biomonitoring. The concentrations of Cd, Cu, Pb, Mn, or Fe measured in buzzards were not toxic. In several places buzzards had recently ingested relatively large amounts Cd and/or Pb. Buzzards with high contents of Cd, Cu, Pb, and Mn were found in areas having more than average contamination. The North-South gradient in aerosol deposition and soil content of heavy metals (especially Cd & Pb) was reflected in the Buzzard. We concluded that the Buzzard is a suitable and cost-effective biomonitor, to investigate the bioavailability of ecocontaminants in large areas, to signal gross changes in food webs, and to monitor raptor persecution.