(HP-65) Free Ca

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An extract of Appendix: Calculation of Free Ca, from Use of a Potential Sensitive Dye in Studies on Phospholipid and Sarcoplasmic Reticulum Vesicles, in Enzymes, Receptors and Carriers of Biological Membranes {A Laboratory Manual}, pgs. 142-144, © by Springer-Verlag Berlin Heidelberg 1984.

"This section describes a simple program to calculate the free calcium concentration in solutions buffered with Egta. It is based on a routine developed by M. Pressler, who was so kind to let us use his notes and saved us the work to develop it ourselves. The program yields reliable results as long as the influence of Mg, ATP, and small cations is negligible. It is based on the following equation:
[free Ca] = [CaEgta] / K' (Ca) * [total Egta]
Where K' (Ca) is the apparent stability constant (pH: 7.0) : 10"'6.312
or often given as log K' (Ca) : 6.312
(The value of this constant is currently under dispute. It is advisable to examine the future literature for updated determinations of it)
p (Ca) : -log [free Ca]
The program runs on a HP 65 programmable pocket calculator. It returns the following results:
[free Ca], [CaEgta], and [free Egta] (all in M)
It is started by the following steps:
1) Type in K' (Ca) ==) press A
2) Type in [total Ca] ) press B
3) Type in [total Egta] ) press C
4) Press D to calculate [free Ca]
5) Press E to display [free Egta]
6) Press R/S to display [CaEgta]

Listing of Program Steps

Before typing in the program steps or entering the program stored on a magnetic card initialize the calculator by clearing the registers, the stack and the resident subroutines (f STK, f REG, f PRGM)

Code:

(-- _:_ ->     Enter K' (Ca) (apparent stability constant for CaEgta) using:
LBL            23             10 ENTER log K' (Ca) g y"x; press A)
A              11
DSP            21    (set calculator display format to 3 decimal digits)
3              03
STO 1          33 01    (store K' (Ca) in reg. 1)
RTN            24
(- - - -)      Enter [total Ca] in M; press B)
LBL            23
B              12
ST0 2          33 02   (store [total Cal in reg. 2)
RTN            24
(- - - -)      Enter [total Egta] in M; press C)
LBL            23
C              13
ST0 3          33 03   (store [total Egta] in reg. 3)
RTN            24
(- - - -)      Press D to calculate [free Ca] from:
LBL            23       K' (Ca) = [CaEgta] / [free Cal * [free Egta]
D              14       (solving of the resulting quadratic equation)
RCL 1          34 01
RCL 2          34 02 
*              71
RCL 1          34 01
RCL 3          34 03    (Calculate: K' (Ca) * [total Cal + K' (Ca) * [total
*              71       Egta] +1 and store in reg. 4)
+              61
1              01
+              61
ST0 4          33 04
f ^-1          32
X^ .5          09  (square above expression and store in reg. 5)
ST0 5          33 05
RCL 1          34 01
f ^ -1         32
x^ .5          09
4              04
*              71   (calculate:
RCL 2          34 02   ((K' (Ca) * [total Ca]+K' (Ca) * [total Egta]+ 1)" 2-
*              71      4K' (Ca) A 2*[total Ca]*[total Egta]) A.S
RCL 3          34 03
*              71
CHS            42
RCL 5          34 04
+              61
f              31
x^ .5          09
CHS            42
RCL4           34 04
+              61
2              02     (calculate [CaEgta) and store in reg. 6)
/              81
RCL 1          34 01
/              81
ST06           33 06
CHS            42
RCL2           34 02  (calculate and display [free Ca))
+              61
RTN            24
(-- --)        Press E)
LBL            23
E              15
RCL6           34 06   (display [CaEgta])
R/S            84
(-- --)        Press R/S)
CHS            42
RCL3           34 03
+              61      (display [free Egta])
RTN            24
               (for next [free Cal in the same solution after adding Ca enter
               new total amount of Ca, press B, press D to calculate new
               [free Cal.

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