Sd. Provan et Md. Miyamoto, UNBIASED ESTIMATES OF QUANTAL RELEASE PARAMETERS AND SPATIAL VARIATION IN THE PROBABILITY OF NEUROSECRETION, The American journal of physiology, 264(4), 1993, pp. 1051-1060
A procedure was developed for dealing with two problems that have impe
ded the use of quantal parameters in studies of transmitter release. T
he first, involving temporal and spatial biasing in the estimates for
the number of functional release sites (nBAR) and probability of relea
se (pBAR), was addressed by reducing temporal variance experimentally
and calculating the bias produced by spatial variance in p (var(s)p).
The second, involving inaccuracies in the use of nerve-evoked endplate
potentials (EPPs), was circumvented by using only miniature EPPs (MEP
Ps). Intracellular recordings were made from isolated frog cutaneous p
ectoris, after decapitation and pithing of the animals, and the concen
tration of K+ ([K+]) was raised to 10 mM to increase the level of tran
smitter release. The number of quanta released (mBAR) by the EPP was r
eplaced by the number of MEPPs in a fixed time interval (bin), and 500
sequential bins used for each quantal estimate. With the use of 50-ms
bins, estimates for var(s)p were consistently negative. This was due
to too large a bin (and introduction of undetected temporal variance)
because the use of smaller bins (5 ms) produced positive estimates of
var(s)p. Increases in m, n, and p but not var(s)p were found in respon
se to increases in [K+] or [Ca2+]/[Co2+]. La3+ (20 muM) produced incre
ases in m and n, which peaked after 20 min and declined toward zero. T
here were also large increases in p and var(s)p, which peaked and decl
ined only to initial control values. The increase in var(s)p was presu
med to reflect La3+-induced release of Ca2+ from intracellular organel
les. The results suggest that this approach may be used to obtain unbi
ased estimates of NBAR and PBAR and that the estimates of var(s)p may
be useful for studying Ca2+ release from intraterminal organelles.