Isoform-specific inhibition of L-type calcium channels by dihydropyridines is independent of isoform-specific gating properties. Mol Pharmacol

ABSTRACT Dihydropyridines (DHPs) block L-type Ca 2ϩ channels more potently at depolarized membrane potentials, consistent with high affinity binding to the inactivated state. Nisoldipine (a DHP antagonist) blocks the smooth muscle channel more potently than the cardiac one, a phenomenon observed not only in native channels but also in expressed channels. We examined whether this tissue specificity was attributable to differences of inactivation in the two channel types. We expressed cardiac or smooth muscle ␣1C subunits in combination with ␤2a and ␣2/␦ subunits in human embryonic kidney cells, and used 2 mM Ca 2ϩ as the permeant ion. This system thus reproduces the in vivo topology and charge carrier of the channels while facilitating comparison of the two ␣1C splice variants. Both voltage-dependent and isoform-specific sensitivity of 10 nM nisoldipine inhibition of the channel were demonstrated, with the use of Ϫ100 mV as the holding potential for fully reprimed channels and Ϫ65 mV to populate the inactivated state. Under drug-free conditions, we characterized fast inactivation (1-sec prepulses) and slow inactivation (3 min prepulses) in the two isoforms. Inactivation parameters were not statistically different in the two channel isoforms; if anything, cardiac channels tended to inactivate more than the smooth muscle channels at relevant voltages. Likewise, the voltage-dependent activation was identical in the two isoforms. We thus conclude that the more potent nisoldipine inhibition of smooth muscle versus cardiac L-type Ca 2ϩ channels is not attributable to differences in channel inactivation or activation. Intrinsic, gating-independent DHP receptor binding affinity differences must be invoked to explain the isoform-specific sensitivity of the DHP block

Genome-Wide Association Study Identifies GPC5 as a Novel Genetic Locus Protective against Sudden Cardiac Arrest

BACKGROUND:Existing studies indicate a significant genetic component for sudden cardiac arrest (SCA) and genome-wide association studies (GWAS) provide an unbiased approach for identification of novel genes. We performed a GWAS to identify genetic determinants of SCA. METHODOLOGY/PRINCIPAL FINDINGS:We used a case-control design within the ongoing Oregon Sudden Unexpected Death Study (Oregon-SUDS). Cases (n = 424) were SCAs with coronary artery disease (CAD) among residents of Portland, OR (2002-07, population approximately 1,000,000) and controls (n = 226) were residents with CAD, but no history of SCA. All subjects were of White-European ancestry and GWAS was performed using Affymetrix 500K/5.0 and 6.0 arrays. High signal markers were genotyped in SCA cases (n = 521) identified from the Atherosclerosis Risk in Communities Study (ARIC) and the Cardiovascular Health Study (CHS) (combined n = 19,611). No SNPs reached genome-wide significance (p<5x10(-8)). SNPs at 6 loci were prioritized for follow-up primarily based on significance of p<10(-4) and proximity to a known gene (CSMD2, GPR37L1, LIN9, B4GALNT3, GPC5, and ZNF592). The minor allele of GPC5 (GLYPICAN 5, rs3864180) was associated with a lower risk of SCA in Oregon-SUDS, an effect that was also observed in ARIC/CHS whites (p<0.05) and blacks (p<0.04). In a combined Cox proportional hazards model analysis that adjusted for race, the minor allele exhibited a hazard ratio of 0.85 (95% CI 0.74 to 0.98; p<0.01). CONCLUSIONS/SIGNIFICANCE:A novel genetic locus for SCA, GPC5, was identified from Oregon-SUDS and successfully validated in the ARIC and CHS cohorts. Three other members of the Glypican family have been previously implicated in human disease, including cardiac conditions. The mechanism of this specific association requires further study

A corrole nanobiologic elicits tissue-activated MRI contrast enhancement and tumor-targeted toxicity

Water-soluble corroles with inherent fluorescence can form stable self-assemblies with tumor-targeted cell penetration proteins, and have been explored as agents for optical imaging and photosensitization of tumors in pre-clinical studies. However, the limited tissue-depth of excitation wavelengths limits their clinical applicability. To examine their utility in more clinically-relevant imaging and therapeutic modalities, here we have explored the use of corroles as contrast enhancing agents for magnetic resonance imaging (MRI), and evaluated their potential for tumor-selective delivery when encapsulated by a tumor-targeted polypeptide. We have found that a manganese-metallated corrole exhibits significant T1 relaxation shortening and MRI contrast enhancement that is blocked by particle formation in solution but yields considerable MRI contrast after tissue uptake. Cell entry but not low pH enables this. Additionally, the corrole elicited tumor-toxicity through the loss of mitochondrial membrane potential and cytoskeletal breakdown when delivered by the targeted polypeptide. The protein–corrole particle (which we call HerMn) exhibited improved therapeutic efficacy compared to current targeted therapies used in the clinic. Taken together with its tumor-preferential biodistribution, our findings indicate that HerMn can facilitate tumor-targeted toxicity after systemic delivery and tumor-selective MR imaging activatable by internalization