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We examined the effect of zinc on rat neuronal nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes as simple heteromers of ␣2, ␣3, or ␣4 and ␤2 or ␤4. Coapplication of zinc with low concentrations of acetylcholine (ՅEC 10 ) resulted in differential effects depending on receptor subunit composition. The ␣2␤2, ␣2␤4, ␣3␤4, ␣4␤2, and ␣4␤4 receptors exhibited biphasic modulation by zinc, with potentiation of the acetylcholine response occurring at 1-100 M zinc and inhibition occurring at higher zinc concentrations. In contrast, ␣3␤2 receptors were only inhibited by zinc (IC 50 ϭ 97 Ϯ 16 M). The greatest potentiating effect of zinc was seen with ␣4␤4 receptors that were potentiated to 560 Ϯ 17% of the response to ACh alone, with an EC 50 of 22 Ϯ 4 M zinc. Cadmium, but not nickel, was also able to potentiate ␣4␤4 receptors. Both zinc potentiation of ␣4␤4 receptors and zinc inhibition of ␣3␤2 receptors were voltage independent. The sensitivity of zinc potentiation of ␣4␤4 to diethylpyrocarbonate treatment and alterations in pH suggested the involvement of histidine residues. Zinc continued to inhibit ␣4␤4 and ␣3␤2 after diethylpyrocarbonate treatment. Application of a potentiating zinc concentration increased the response of ␣4␤2 and ␣4␤4 receptors to saturating ACh concentrations. The rate of Ach-induced desensitization of these receptors was unaffected by zinc. Our results reveal zinc potentiation as a new mode of neuronal nAChR modulation.

Background: The R21C substitution in cardiac troponin I (cTnI) is associated with hypertrophic cardiomyopathy in man. Results: The R21C mutation disrupts the consensus sequence for cTnI phosphorylation. Conclusion: The KI mouse model showed remarkable degree of cardiac hypertrophy and fibrosis after 12 months of age. Significance: One of the physiological roles for the phosphorylation of the cTnI N-terminal extension is to prevent cardiac hypertrophy.

Two novel mutations (G159D and L29Q) in cardiac troponin C (CTnC) associate their phenotypic outcomes with dilated (DCM) and hypertrophic cardiomyopathy (HCM), respectively. Current paradigms propose that sarcomeric mutations associated with DCM decrease the myofilament Ca 2؉ sensitivity, whereas those associated with HCM increase it. Therefore, we incorporated the mutant CTnCs into skinned cardiac muscle in order to determine if their effects on the Ca 2؉ sensitivities of tension and ATPase activity coincide with the current paradigms and phenotypic outcomes. The G159D-CTnC decreases the Ca 2؉ sensitivity of tension and ATPase activation and reduces the maximal ATPase activity when incorporated into regulated actomyosin filaments. Under the same conditions, the L29Q-CTnC has no effect. Surprisingly, changes in the apparent G159D-CTnC Ca 2؉ affinity measured by tension in fibers do not occur in the isolated CTnC, and large changes measured in the isolated L29Q-CTnC do not manifest in the fiber. These counterintuitive findings are justified through a transition in Ca 2؉ affinity occurring at the level of cardiac troponin and higher, implying that the true effects of these mutations become apparent as the hierarchical level of the myofilament increases. Therefore, the contractile apparatus, representing a large cooperative machine, can provide the potential for a change (G159D) or no change (L29Q) in the Ca 2؉ regulation of contraction. In accordance with the clinical outcomes and current paradigms, the desensitization of myofilaments from G159D-CTnC is expected to weaken the contractile force of the myocardium, whereas the lack of myofilament changes from L29Q-CTnC may preserve diastolic and systolic function.Cardiomyopathies are diseases of the myocardium that often lead to cardiac remodeling to compensate for deficiencies in cardiac output (1). In the case of dilated cardiomyopathy (DCM), 2 heart failure is characterized by a systolic dysfunction (i.e. reduced ejection fraction), whereas hypertrophic (HCM) and restrictive cardiomyopathies are characterized as having diastolic dysfunctions (i.e. impaired relaxation) (2). In many cases, the cardiac contractile dysfunction is attributed to inherited sarcomeric gene mutations. The functional effects of more than 40 thin filament mutations associated with cardiomyopathies assessed in vitro suggest that these mutations affect the Ca 2ϩ responsiveness of the myofilament in the absence of CTnI phosphorylation. As the number of in vitro-characterized mutations continues to grow, a developing paradigm emerges that associates decreases in the myofilament Ca 2ϩ sensitivity with DCM (3-7) and associates increases with HCM (4, 6 -12) and restrictive cardiomyopathy (13)(14)(15)(16)(17). This suggests that distinct effects on the Ca 2ϩ -dependent processes of the myofilament are critical determinants of the severity and molecular pathologies of these diseases.The first cardiac troponin C (CTnC) mutation (E59D/D75Y) was found in an explanted heart from an adult male who died fr...

Mutations in sarcomeric proteins have recently been established as heritable causes of Restrictive Cardiomyopathy (RCM). RCM is clinically characterized as a defect in cardiac diastolic function, such as, impaired ventricular relaxation, reduced diastolic volume and increased end-diastolic pressure. To date, mutations have been identified in the cardiac genes for desmin, α-actin, troponin I and troponin T. Functional studies in skinned muscle fibers reconstituted with troponin mutants have established phenotypes consistent with the clinical findings which include an increase in myofilament Ca2+ sensitivity and basal force. Moreover, when RCM mutants are incorporated into reconstituted myofilaments, the ability to inhibit the ATPase activity is reduced. A majority of the mutations cluster in specific regions of cardiac troponin and appear to be mutational “hot spots”. This paper highlights the functional and clinical characteristics of RCM linked mutations within the troponin complex.