Making and Using Calcium-Selective Mini- and Microelectrodes - Methods in Cell Biology - page 87

used to titrate the passive Ca 2 þ binding sites in permeabilized myocytes where the
cellular Ca 2 þ uptake and release process are inhibited. The same titration method
has also been used to measure total Ca 2 þ uptake in the SR of permeabilized
cardiomyocytes ( Hove-Madsen and Bers, 1993a ).
Ca 2 þ minielectrodes have also been used together with indo-1 for online mea-
surements of the Ca 2 þ uptake rate in the SR in permeabilized ventricular myocytes
( Hove-Madsen and Bers, 1993b ), to examine the e

ects of phospholamban phos-
phorylation and temperature ( Hove-Madsen et al., 1998; Mattiazzi et al., 1994 )
and to measure the number of SR Ca 2 þ pump sites by titration with the selective
pump inhibitor thapsigargin ( Hove-Madsen and Bers, 1993b; Hove-Madsen et al.,
1998 ). In these applications, the electrode response time can become a limiting
factor and it is important to use a fresh Ca 2 þ electrode for each experiment, and to
minimize inhomogeneities in cell suspensions that the calcium electrodes cannot
detect.
Although the use of Ca 2 þ selective electrodes for measurements of dynamic
changes in some biological systems is limited by their response time (particularly
at submicromolar concentration), the potential benefits of combining Ca 2 þ selec-
tive electrodes with other experimental techniques are underexplored. Indeed,
calcium selective electrodes have successfully been used to monitor [Ca 2 þ ] inside
patch pipettes ( Kang and Hilgemann, 2004; Kang et al., 2003 ). New Ca 2 þ sensors
based on coating of microcantilevers with ion-selective self-assembled monolayers
have also been developed ( Ji and Thundat, 2002 ) and may be useful in the mapping
of Ca 2 þ channels and transporters on the cell surface. Indeed, measurement of the
change in extracellular ion concentration with ion-selective MEs has also been
shown to provide a noninvasive means for functional mapping of the location and
density of potassium channels ( Korchev et al., 2000; Messerli et al., 2007 ) and for
the quantification of transmembrane Ca 2 þ flux ( Bers, 1983, 1985, 1987; Bers and
MacLeod, 1986; Shattock and Bers, 1989; Smith et al., 1999 ).
Thus, in spite of the overwhelming predominance of fluorescent Ca 2 þ indicators,
Ca 2 þ -selective electrodes and biosensors still remain a valuable supplement to
many imaging and electrophysiological techniques in molecular and cellular
physiology.

V

Acknowledgments

This work was supported by a grant from the National Institute of Health (HL30077) to DMB and a
grant from the Spanish Ministry of Science and Technology (SAF2007-60174) to LHM.

References

Allen, P. D., Lopez, J. R., Sanchez, V., Ryan, J. F., and Sreter, F. A. (1992). EU 4093 decreases
intracellular [Ca 2 þ ] in skeletal muscle fibers from control and malignant hyperthermia-susceptible
swine. Anesthesiology 76, 132-138.

Ammann, D. (1986). Ion-Selective Microelectrodes. Principles, Design and Application Springer,
Berlin.